I'm tempted by the dual 2.5, but I'll probably wait for the Rev. C as well, PCI Express being one of the main reasons. It's already working its way towards technology's dustbin, everyone (except Apple so far) is moving to PCI Express. I think it's safe to say you're going to have a very hard time finding PCI-X cards in four years time, or even two years time if you're shopping for high-end graphics/video cards. I need to see some innovation on the PowerMacs before I drop three grand on one: PCI Express, two FireWire 800 ports (preferably on separate controllers), more internal space for hard drive storage (4-5 bays), a design that does not require blocking a slot to install a high-end graphics card (and 4 slots would be nice too), and for Pete's sake fix the bloody chirping/audio problems. Plus more trivial things like a keyboard and multibutton mouse that actually match this machine, and not one manufactured five years ago.
2.5 GHz is not a problem, the other stuff is.