I can certainly 'weigh' in on the 1//2 length bag discussion here. I used one made by Mike for 50 days walking the South Island of the TA. After much debate and discussion Mike and I settled on 140cm for the length and for me at 175cm I find it is perfect. I wouldn't want it much shorter definitely. In terms of weight saving I think there is a significant benefit, but only when temperatures are mild (this was a +4C bag).
I paired it with a Montbell Down Jacket (1000 Plasma one) and then layered a wind vest on top of that also. It kept me warm in NZ. I could tell if it was any colder it would have not been sufficient but in that situation it worked well.
I can also certainly say I like the hoodless mummy style being a massive fan of my -12C Zpacks one, and am in the process of discussing with Mike a 0C one right now!!!