lower clock doesn't mean lower heat
it has to do with number of transistors, core voltage, and a few other thigns
Intel's new dual core is as hot as a PAIR of 3.2E's
it's pushing 130W
the 3.2E is around 75W
your seriously wrong
dual Xeon's would do better, but only because dual Xeon's would have more clock on the 840 (if your comparing best to best)
aside from that, dual processor MB's are no more expensive than single proc dual supporting mb's are...please understand
a PC-DL (Asus' dual Xeon 604 board, it supports AGP 8x which is it's selilng point, it's also ATX compared to the de facto standard of eATX for dual Xeon's)
but a PC-DL is around $170
a new 955X equipped board is probably going to be around $220...
the cost is saved in buying 1 840 compared to two 3.6 Xeon's (an 840 is like $1000, the 3.6 Xeon's are like $700 each)
the 840 is able to out-render any P4 iirc
including the 570J (currently it's the fastest of the single core P4's, even over the 3.73EE, which won't do well with the 840 just being released)