gkay, the 860 maybe faster, but 920 supports triple channel. Turbo mode, it's joke if your just going to OC, which pretty much renders most of the p55 perks moot.
Turbo has to stay in the thermal envelope.
syxx, no, it's fine for a single card, i'm personally a little iffy on my knowledge about the 2 x8 lanes vs full x16 lanes, but from what i've seen/heard, there isn't much of a difference, even on quad sli/quadfire.
I'd check your case size, but a v8 works great for me, but scythe and xigmatek both make great coolers. Whatever you do, don't waste money on a v10, it's a waste of money, RAM cooler, you don't really need it.