Just my 2 cents, I've been overclocking for about 10 years, and have done many experiments with air flow and the like. I have found the negative pressure cooling is more efficient from a purely air flow standpoint. (Tends to suck in the dust tho hehe.) In my antec 902 case, I took out the side intake fan (on the clear side), and installed an 80 cfm slot fan under my gpu, over the psu in the back. The net effect of this is now I have a jet stream of cool air running through the bottom half of my case, while the top 200 mm, and rear 120 mm actually tap that stream to cool my cpu and help the push-pull cooler exhaust straight out of the case. My case temps are cooler, cpu temps are cooler, and It takes far less time now to cool my entire machine down after a hard run of folding (less than 5 minutes), and I got higher overclocks out of the deal too.