[zoson]

Ok, my system is ALMOST exactly like what you're describing. I run an ADDA 116CFM 120mm fan on my blowhole, which is on the radiator. *But* for quiet sake, I keep all my fans throttled with my rheobus. I would say that the 120mm is only pushing around... 40-50CFM. I have to say that the BI-X performs admirably even without a 100+CFM fan. That was Chip just talking out of his ass. With my fans throttled, my computer will idle at about 35C with an ambient of 28C. With the fans full blast, the ambient in the case will drop to about 25C and the cpu temp will drop down to about 29-30C.
I see absolutely no need to move the hd rack back. It would be more wise to move the psu to the top, put the radiator where the psu is now, and keep your resivor where it's at. But even that is a little extraneous. You could save yourself a lot of work and put a 120 where the top two 80mm fans are for exhaust, and stick your radiator there. That way hot air will be going OUT of your case, and not into it. As long as you leave your hose barbs at the top of the radiator, the bubbles will not say in the radiator. If you leave your resivor where you have it, it will be at the highest point and you're good to go.
-Zoson