If it's stable then it's probably not worth messing with. If you are obsessive like me though then by all means post a diagram and I'll see if I can spot any things I would change.
Is the GPU block one of the newer DD ones or the really really old school one? Their first one was a flowrate killer!
What motherboard are you using?
Might want to try setting up Speedfan if the motherboard supports it. You could then use a higher power fan connected to the CPU fan header and then let speedfan PWM it depending on CPU temp. I have my AMD box set up like this now: it's very quiet idle and around 38-39C (40% fan speed) and ramps up so it's spinning at 100% around 50C. Works great. Gotta make sure that your mobo header can handle the W of the fan though
