It's also a bit difficult. With Apple actually being the _sole_ computer vendor to actually make use of the PowerPC as a desktop and notebook processor (yes, there are others, but they are _very_ small players and for this thought don't even matter), we only see what IBM can deliver if Apple shows us. IBM, for what it's worth, could deliver a G5 notebook processor running at 2.5+ GHz right _now_, and as long as Apple doesn't produce a computer that makes use of it, for what we know, IBM didn't deliver.
Once Apple jumps boat, IBM simply _won't_ deliver desktop and notebook PowerPC processors. And we won't know where they would have driven. We'll only see what they'll do with the POWER series and with the console chips (and those are updated every other year at best).
Btw.: I thought we already discussed this about two weeks ago or so...