In Conclusion
This cooling arrangement is much more effective, and peaceful, for dual processor machines than the first setup. The heat generated by these two CPUs, while low compared to the G5 machines, was simply too much for the 80mm radiator solution to cope with peacefully, and as such fans were often running noisily to keep the system cool. Now, with a reduced number of fans, temperatures are kept lower with less noise and more headroom for sudden spikes in processor usage. All this and the machine is externally identical to when it was first made.More Twiddling
The problem is, once you start, you see what else could do with changing. With the ATI 9800 Pro installed this system is entirely complete, runnning cooler and more quietly than ever. However, the (even quieter) nVidia 7800GS can reach 68 degrees under sustained use - not a problem for the graphics card, but it is for the power supply, as that hot air is vented straight to the front of the case from where the PSU is supposed to take in cool air for itself.One solution to this would be to provide a new air intake for the PSU, which is something I'm considering doing in the future. However, such temperatures only become a problem when giving the 7800 a lot of hammer, as it generally receives a good amount of cool air from the CPU section below. The temporary solution I've come up with in the meantime is just to open the door when playing Doom 3, which is the only app that's managed to generate such high temperatures so far. It's a stopgap that will do until I have some more free time and can get some new parts made...