Thanks Mike, it's not a big deal if it's lots of effort to investigate etc.
If it helps much of my write up in VF-900 thread
is also missing.
monk, yes your plan for PSU fan should work out ok, as you say the PSU will see higher temp/load when the CPU and GPU are loaded.
The PWM fan may work connected to the PSUs fan header, some PWM fans are ok with voltage control and others are less so. Usually dropping rapidly in speed in the 11-7v range and then holding on to a certain minimum. You'd need to test it on a fan controller or 3 pin motherboard header to see.
I think when you use a slower fan on the PSU's header all that happens is the temp/fan speed curve is moved, for example with new slower fan the internal temp for 200w would be the same as with original fan at 300w. Same temp = same fan voltage but if you swapped 2000rpm fan for 1300rpm fan you would have a lower fan speed, you're swapping cooling for noise and as long as not pushing the PSU limits it'll be fine.
$20 seems like a lot for a fan, where are you located? I like Arctic Cooling F fans as cheap and quite good, F12 is <£5 here. Also Xilence Redwing is good cheap fan and Nexus is only £6.25, about the same for Gelid Silent 12 from QuietPC, who I think ship internationally.
Good luck, Seb