Well, I believe it is the processor causing most of the heat only because, my system temp stays in the red (high) I'm pretty sure it's not because of the PSU only because it has two fans, one intake and one exhaust. The air coming out of both PSUs is rather warm. I just checked both of them.
The system temp on my opty machine is nice and cool. It's not necessarily a fair comparison as, in the Intel machine, I have more hardware in it such a TV tuner card, modem, extra hard drive, 2 DVD burners and a sounblaster audigy2 ZS. I'm sure those things put out a little more heat.
On the flipside of this though, I do have a side intake fan on the Intels case so it does have an extra fan. The opty machine doesn't have one cause of the CPU cooler. It extends too far to install a side case fan.