OK. So let me get this straight. I should buy an A1G3XE 800Mhz and not the A1G4XE 800Mhz because it's slower or less powerful?
I'm confused! Or are you saying that the full advantage of the G4 is not used becasue of lack of support for that processor? Surely it would be better going for the G4?
If it's down to power and heat then that should not be a problem. I have two PC's here which I can guarentee get a lot bloomin hotter! I'm well used to having 4-10 fans inside a tower. As for PSU's 300W should be ample and if not get a 400w or more.
If there is no advantage with getting the G4 over the G3 then I would also suggest that the G3 would be a better choice and then upgrade. However, with the price difference I would still go for the G4 even if it was only marginally faster.