Its up to you Esse. It depends on how much you care about noise. Now I don't particularly care too much about noise so I bought that vantec tornado thinking the people saying it was loud were whiners, cause they said that about the coolermaster jet and it doesn't bother me. the thing is INSANELY loud. Theres a difference between 'not caring about sound' and 'how long do you think your sanity will last with a constant hair dryer going' Imagine if you had a sister blow drying her hair all day while you were at the computer hehehe thats just ONE of those fans muchless two or more. Plus I got the 80mm one, I can't imagine what the 92mm sounds like. You could use the 92mm tornado on an SLK-900a heatsink and since its in the case you might not hear it that much plus you should get phenominal cooling from that. Plus if you get a rheobus controller, that thing is strong enough to handle those tornados, BUT that controller also has the option to turn your fan OFF so if other people use your computer and you have the controller hooked up to your CPU then just be careful.
Try and keep the dBa as low as possible while finding the highest possible CFM. Once you start getting past like 50-60 CFM though the fan is gonna be loud regardless. tornado is 84cfm with like 55dBa and that is LOUD as hell so definitely go for 40 and under as far as dBa goes