I've got the 24" and recently bought a 16" upper to go with it. Honestly, I can't see too much difference in the accuracy between the two. Both uppers have shot many cloverleaf patterns at 100 yds from the bench. The 24" likes Federal 168 gr Match, and the 16" likes Winchester 168 gr Silvertips best. The extra 4 lbs or so on the 24" soaks up a lot of the recoil, but in either configuration, the recoil isn't anywhere near as stout as my 308 bolt guns.
I was toying with the idea of cutting down my 24", but decided to leave it as is for antelope hunting out west since it stays in the truck until I see something worth shooting at and bench rest. I'm using the 16" as my brush white tail hunting gun/SHTF now, and I LOVE IT!
I don't want to sound like a DPMS whore, so here's some negative input--My 16" short stroked the first 500 rds or so and had to be sent back to the factory for repairs. I got it back in about 5 days, which I would normally call fantastic service, but it came back with the same problem. I wound up installing a Fulton Armory adjustable gas tube ($60) and haven't had a problem since.
I've got about 2K through the 24" without a hiccup, and about 1.5K through the 16"--first 500 were frustrating as hell, after the gas tube fix, the last thousand were a complete delight. Just make sure you get some steel mags with yours--the plastic ones mine came with SUCK! Feed lips crack if you look at them crosseyed and rarely feed properly. I bought SR25 mags ($125 each) for mine, but the steel DPMS 20 rd mags are supposed to be available next week.
Keep us posted!