Here is the table of upcoming Intel CPU designs. It seems that Yonah 2 will be out in early 2006. Just in time for the OSx86 consumer debute. They've also got a NetBurst upgrade and and Enterprise level chip upgrade at the same time. Thus it seems Apple will be using the Yonah 2 or a late Pentium M to power the new x86 Macs if they want to keep up the "power-per-watt" justification.
This is just idle speculation based on a Slashdot article I read. If the rumor mills picked up the theme and ran with it, I haven't read it yet... It's pretty easy to draw my conclusion by looking at the Apple x86 schedule and the Intel schedule and looking for similar ship dates.