So I find myself probing you guys for all sorts of info, not just lightweight stuff, because I don't think theres another forum with as much knowledge as there is to be found here. Now that I've sucked up the proper amount, my question.

Been looking at Feathered Friends 35 deg. Rock Wren http://www.featheredfriends.com/Picasso/Bags/Specialty.html A long weighs in at 29 oz. For those not familiar, the Rock Wren converts from a sleeping bag into a parka of sorts via two arm holes and a cinchable bottom. Gone would be cold mornings shivering while eating breakfast! I'm hoping the ventilation for summer heat would be as good as a full zip bag (which this is not) because you could sleep with your feet and arms out of the bag. I plan on using this bag for everything from Northern New Jersey to the high country of Wyoming, increasing my clothing as it gets colder.

Thoughts, warnings, etc? I may ask for 2 oz of overfill, heard theyll do that and other custom trick outs. I've read that this company's temp ratings are actually quite on, but just in case, I may opt for the tiny bit of overfill (they use 850+ down).

I have never used the wren bags but I have spent many a night and morning in my FF Vireo bag with either the Volant or Helios jacket. Great system.

The last Vireo bag I got, I had FF make the baffles larger and add overfill. This was done after they advised it. I was told that this is a better approach to increase the bags temp compaired to just adding more fill. They charge a $50 "custom fee" then whatever the costs of your extras are ($10 per ounce of extra down).

I have 3 FF bags and 2 of thier jackets. Top notch.

I would also look into the Jacks-R-Better "stealth" quilt if I were you. Similar to the wren bags but in quilt form.

(I may be selling my 62" Vireo as I will be purchasing a quilt with the same temp rating) <<< shameless plug

I've had my Rock Wren since 1999. It is a long with standard nylon shell and weighs in at 31 ounces in the stuff sack so I think the 29 ounce figure is accurate.
The current materials are better than what was available ten years ago. The bag is extremely well made and I have been very happy with it. I have not used it nearly as much as I wished and can't attest to a huge variety of temperatures. I last used it at Whitney trail camp in June of 2010 inside a Goretex bivy of the same vintage. I think temps got down to 25 or so and I was snug in lightweight Capilene top and bottom. The bottom opening is nice for venting and shoving your arms out through the shoulder zips is really helpful when things get warm. Never had occasion to wear it around camp but I'm sure it would work great. It is a narrow bag, FYI.

I have a Rock Wren with +2 oz. of overfill and the epic shell. As the previous posts indicate, FF construction is top-notch.

I purchased mine in '99/00 with the thought of dropping some pack weight by wearing the bag around camp in place of a jacket. This feature is great for frosty mornings or when you have to get up to empty the bladder at midnight. But I found that I rarely jettison the jacket as I intended. I find that a jacket is just more convenient. When you're wearing the Rock Wren as a vest/jacket there is a lot of sleeping bag around your torso that can obstruct your vision as you cook/eat, pull out stakes, etc. You can flatten the bag easy enough but it is something that you will have to do in order to see and have to do frequently. I don't think the sum of this paragraph is either pro or con, just my experience and how I use it.

The jacket is also more convenient for those cold, windy lunch breaks when a windshirt will not be enough. I really don't want to pull my sleeping bag out from the bottom of my pack for that use.

It makes a great sleeping system when combined with a light down jacket/pants to extend the temp rating.

Also, when it's really cold out, I intuitively get into a "mummy bag" posture--legs together or crossed. But when it's warmer, such as the temps the Rock Wren would be used in, I like to be able to spread out some and the bag has plenty of girth in the legs to allow this.

I would definitely recommend the 2 oz. of overfill and honestly, it could handle 3 oz.

Thanks guys. @Ty I plan on ditching a fleece, or bringing a super light weight fleece if anything, by using the bag. A good soft shell goes anywhere, whereas the bag is definitely not for the trail. So ventilation wise, no sense going for a full zip when the arm and leg holes will allow for a good amount of vent?

I just got a Winter Wren and have used it exactly three times -- on my mother's couch! So I'm not much help to you yet.

I'll be taking it out mid-April though, so if you haven't purchased by then, I'll have more to say then.

Anyway, I found it too hot on Mom's couch, but venting it didn't seem to be a problem -- as you know the zipper runs down the front of the chest. I find that excess heat vents up and out without leaving me chilled (I had a light cotton shirt on). My summer bag has a half-zipper too, on the side, and that vents just fine, imho.

I don't expect to hike or even move around camp much in it, but on those winter nights when hiking and cooking is finished early and I'm sitting still and shooting the... breeze... around the campfire with my friends -- that's when I tend to get cold and wish I had something on over my jacket.

So... we'll see. I CAN say that it seems to be very well made, is light as a... feather... and very fluffy and cozy, fwiw.

I understand your concern with the full-zip vs half-zip temp regulation. Aside from sticking your legs out or opening the foot and pulling the bag up, your legs will always be surrounded by down in the Rock Wren. So you cannot adjust the lower body temp as well as you could with a full-zip. However, it would be a very narrow temp range in which this would be an issue (IMO) as there are other venting/temp adjustment options. As previously mentioned, the wider girth in the leg area is a non-venting means of temp regulation--you can sleep with your legs further apart than a mummy bag allows, increasing surface area and allowing you to radiate some lower body heat. As the zipper is centered on top, you can easily and rapidly vent some heat from your core. The down is distributed 60/40 top/bottom so you can unzip and use the bag as a quilt in warmer temps. Then there is the drawstring foot and the arm holes to play with as well.

A note for when the temps are colder: The draft tube is more than adequate so there's no need to worry about losing heat through the center-located zipper. There is some heat loss at the arm holes even when zipped. Since the bag is rated to 35 I never use it at temps where this would be an issue.

One more thing to consider when purchasing a Wren. Make sure the length is adequate for your height WHEN THE FOOT IS CLOSED. I'm 5'10" and so get a size regular (6'0"). It was obvious that FF did there length measurement with the drawstring open. I could make-do but the bag was too snug even though I am 2 inches shorter than the bag was sized. I had to return that bag do to some delaminating issues and the bag I received in exchange fit well with the drawstring tight. Maybe FF made this adjustment--I'd confirm with them when you place your order.

I'm sure all of that could have been said much more succinctly. Sorry for the many words.