A few notes...
Long Sleeve: You're worried about the L/S in summer. The main benefit of a L/S in summer is sun protection (minimizes amount of sunscreen you need to carry). Since you have a windshirt and will probably wear it most of the time, you can most likely ditch the l/s. If you still want, I'd recommend the light gray Phase SL longsleeve from arc'teryx. Mine weighs 3.8oz and I can wear it in the summer out here (AZ Desert Rat). It dries incredibly quick, feels durable for the weight, and so far odor-less after a couple days of heavy wear (haven't done a full week in it).
Insulation: I was just given a M.B. Down Inner Parka. A bit late out here, so I haven't field tested it cool conditions. What I do know is that it only weighs 8.2oz in medium (others have also commented that it runs a bit light from the spec). Having a hood and supposedly .5oz more down than the jacket...I would suggest just moving up to it. That hood will provide lots of versatility and warmth (40F quilt should work well enough even if you get caught in a summer blizzard). It also only costs you $20 and 1oz to do so.
Head Warmth: Regardless of a down jacket or parka, you still want a separate warm head piece for while on trail. The Possum Down looks like a great option and minimal weight. I'm a personal fan of Buff Headwear. If you don't know what it is, it's basically a tube of fabric that can be worn as a beanie, balaclava, scarf, and dozen other configurations. The Merino Buff weighs 1.8oz, has a lot more length than the original (so may be able to cut in half) and is that wonderful warmth/coolness that is wool. Depending on how you wear it it'll keep your head warm and the sun off you.
I get cold easy though, so if it seems like warmth overkill, the regular buff could also work. I wear the regular religiously in the desert during summer as a balaclava. Keeps the sun completely off my skin, dust out of my lungs/eyes, and, most appreciated, creates a humid microclimate for my mouth/nose. This creates an evaporative effect that cools incoming air with every inhale. It also dramatically reduces how much liquid I lose due to respiration and is great for maintaining hydration in bone-dry desert and alpine air. I never understood why Bedouin's were so completely wrapped up until I forgot sunblock in Death Valley and tried it out for myself, I was an instant convert.
I forgot to mention trekking poles. I use the the LT4s from Gossamer Gear and love them. On flat ground I don't really weight them much, so don't get that speed boost of pushing off with them. But for all ups and downs I rely on them heavily. I had some ITB and knee problems when I first got back into hiking and they were invaluable in easing the pain in my legs. You may find that once you get used to them you feel "fresher" at the end of high mileage days. Granted my poles weigh only 7.5oz combined, not over a pound. I don't think I would like traditional heavy poles because of the heavy swing weights requiring more upper body energy expenditure.
I would suggest some experiments. Do a long day hike you're familiar with with the poles, then the next weekend do it without poles. Try to eat the same and have similar weather if possible. Time your hikes and take notes on how tired you feel after each one. This does give the advantage to no poles (since you should build/maintain muscle mass from the first hike with poles). If no significant difference or they just annoy you, don't bother. If you see some benefit then you can take them with you.