Mitchell (and Ben),
Sorry to take so long to get back to you.
I bought both the LightSpeed and the Jam2 about two months ago. Because I've been so busy with work I haven't had a chance to take either one of them out for a real hike, but did manage to use the LightSpeed two times for some overnight travel to a friend's place. I also have the Ghost, which I've been using for over three years now and really love, so I can make a good comparison.
The LightSpeed is lighter than the Ghost and has roughly the same volume, though the LIghtSpeed is narrower and taller. When packing for some reason the Ghost seems to take bulky items, like a sleeping bag or tent, more easily; they just slide in as they should. The Ghost has more robust fabrics than the LightSpeed, too, and can easily handle offtrail walking, but the material of the LightSpeed is quite substantial. It feels slick and makes me wonder if perhaps it is more waterproof than the Ghost's.
Like the Ghost the LIghtSpeed has a weatherproof zipper that also opens 3/4 of the way. There are four compression straps on the sides, rather than just two, like on the Ghost, and that is one plus in helping to stabilize the entire load. And unlike the Ghost there is a HUGE front pocket, in addition to the bungee straps, that can take quite a lot of gear. SInce I like to keep my shelter, windshirt, and toilet kit outside here, it is the perfect addition that I always felt the Ghost was missing (and therefore I sewed on a mesh front pocket). The side pocket on the Ghost are wonderful, just right for a water bottle and easily reached when wearing the pack. The side pockets on the LightSpeed, however, are tiny, just barely tall enough to take a water bottle and even then I had to add a cord to my water bottles that attaches to the lower compression strap so that the water bottle doesn't fall out. This, of course, defeats the purpose of being able to reach back and take out the water bottle while walking, so I will have to think of some other way to secure the waterbottles in the pockets. The hipbelt pockets are a wonderful addition on the LIghtSpeed that I always wished the Ghost had (I did jury rig two add-on small size Granite Gear Air Pockets with bungee cord... wasn't quite ready to sew pocket on yet, as per Ben's suggestion on another site, since I hadn't found pockets that I really liked). They are just big enough for the items that you need there and are positioned well back so they don't interfere with the swing of your arms. There is an additional pocket on top of the LIghtSpeed that is quite ingenious... sort of an uner-the-hood top pocket that you access from the back though a zipper. The LightSpeed has two aluminum stays that make for a very stiff pack, but also add quite a lot of weight. I think they work better than the Ghost's stays, in that they don't dig into the small of my back when the hip belt is tightened. That being said, I much prefer the suspension system of the Ghost; it just feels more secure and seems to fit more snugly to my back and hips. The LightSpeed always feels as if it is about to roll to one side or other, though, of course, it doesn't. The shoulder straps on the Ghost always felt as if they were there just to stabilize the load and the hipbelt took most of the weight, whereas the LightSpeed, with the hip belt pockets situated well back and therefore the padding over the hip bone just barely covering the hip with 1 1/2 inch nylon webbing, just feels less supportive. Also, since the entire back of the LightSpeed is one continuous 3D Mesh panel it will most likely be much hotter than the Ghost, which has so few contact points on the back.
One of the things I didn't like about the Ghost was that it needed constant readjustment to stay comfortable. I found myself on my hikes stopping every hour or so to readjust the shoulder straps and hip belt, to get it just right. In spite of that I really like the Ghost and often think of buying another one just to have before they are all gone.
When I carried (quite a substantial amount of, certainly more than 20 lbs) weight in my visit to my friend's home (this wasn't a backpacking trip) the LightSpeed did quite well with the weight, as long as I used the stays. It didn't handle the load as well as my Ghost would have, though. Again, the hip belts and way it wraps around the back makes it not as comfortable as the Ghost. Without stays, I wonder what it can do... haven't tried it yet.
For my upcoming trip in the Alps in Europe this summer I'm torn between three packs: the BPL Arctic Pack I just bought, the Jam2 or the LightSpeed. I think I've eliminated the Arctic Pack for this trip. It is simply too much for a trip that will also require time in towns, restaurants, planes, and hotels, and too floppy without its stays. Jury rigging side pockets just seems like added complication, and I want to keep things simple. I'll save it for a trip that will only involve backpacking.
That leaves me with the Jam2 or the LIghtSpeed. I like the simplcity and lightness of the Jam2, but it doesn't have hip belt pockets and has to be accessed from the top... quite a hassle when customs is digging through your stuff at the airport. Still, the Jam2 could make for quite a compact package that the airlines might possibly allow on board, though I'm not sure what they will allow these days.
The LIghtSpeed, with its stays removed is quite a bit lighter and feels more secure. Just not sure how to make a virtual frame this way, though, unless I use an inflatable pad like the MontBell UL pad, folded lengthwise along the back and front of the pack, and blow it up when the pack is closed.
I'll just have to go on a trial hike before I leave and see which of the two works better for a month of traveling and hiking.
Wish I could take my Ghost, but it is just too bulky for a trip like this and is missing features like the hip belt pockets and front pocket.