Will these be the same chips expected to be used in the updated Mac Pro? If so, am I reading this correctly that they actually might be a little slower than the current offerings?
http://www.electronista.com/articles/07/11/07/hp.penryn.xeon.desktops/
"The xw6600 and xw8600 will use the upcoming Xeon 5200 (dual-core) and Xeon 5400 (quad-core) in twin sockets to include as many as eight cores in a single system; the smaller 45-nanometer manufacturing process for the chips improves their performance while also reducing heat and power draw. Professionals can juggle intensive modeling and image editing programs without a significant speed drop, HP says."
It's possible Apple may go for the 1600MHz FSB processors rather than the 1333MHz ones HP are going to be offering, as Apple aren't likely to update the range before Nehalem after the new ones, and would want them as fast as they could offer.
As for speeds, the quad 2.83GHz has the same pricing as the dual 2.66Ghz Apple currently use. So expect faster speeds regardless if the base price remains $2500.
edit: misunderstood what was meant, but my point remains.