i have a couple of 120mm deltas that i plan on using in the 'summer' (in the UK - so summer is a loose description for a couple of warmer than normal weeks )
Hmm, 80% isn't too bad, it can be loud, but not leaf blower loud. I'd look into obtaining a replacement fan, or an aftermarket cooler (locally I've seen seen Arctic coolers for 5850's going for about $20). I'm not sure how well a 120mm delta will cool an reference-style card unless you take off the shroud and strap a couple onto the heatsink, that actually may work pretty well
i was going to use it to pump air into the case but as i'm adding an additional card on risers and having two 220mm fans to blow onto/into the system they may well end up being redundant - my office is 10x6 and i have a small airconditioning unit that i may use but obvously running that 24/7 will increase my operating expenses
i ahve just checked and in the middle of the day the GPUs are at 83 and fans are at 100%
open case will have to be finished this week or i'll have to dial down my GPUs