I replaced all the fans in my QS with Noctua ones. However, I made sure the PSU fan still had a good static pressure rating as I reconfigured the PCI case fan to blow air into the case, not extract it. The standard configuration of the fans is a bit odd, you have a small 60mm fan drawing air in over the cpu heatsink, a 120mm fan and 80mm fan drawing air out. There is very little air being drawn into the case and the intake to exhaust ratio seemed very unbalanced. The way the 120mm fan exhausts air is also bound to add noise as it blows air over 2 sets of perforations, resulting in loads of noise. The ‘airbox’ for the 120mm fan with the small 90 degree flow path is bound to push air back into the case.
So my final solution is a 3,000rpm 60mm fan cooling the cpu via cool air intake, more than enough. The gpu gets hot so the 120mm fan blows cool air over the pci slots at 1,200 rpm. The 80mm psu fan extracts at 2,000 rpm to deal with psu heat and residual case heat. I’ve also cut the metal perforated finger guard out of the psu fan extract path as you already have the outer case guard - no need for double protection.
After some prolonged gaming the case is cool, internals are cool and best off all the system is MUCH quieter.
Cpu is 867mhz.