Well, sure, if you're talking about 970FXs at similar clock speeds. On the other hand, we can't be sure how heavily modified these processors were modified to get them to such low power consumption - they could be even slower, or even faster.

Hmm... perhaps Apple's differentiation between the iBooks and Powerbooks will be dual-core Yonahs in the latter, and single-core PowerPCs in the iBooks? That would be kinda cool, although I'm aware it'd also probably be a terrible way to go.