As you can see 2.66 is replacing 2.53 with the same 6Mb cache, then 2.4 > 2.53 (3Mb), and 2.0 (which had to be 2.26 BTW) going to become 2.4.
That's at least what Intel is doing (Introducing new top CPUs & dropping previous in price brakets - Announced Dec 30'08).
Now of course it's for Apple to pass this new tech (or savings if they decide to keep old ones (yeah, that's definitely NOT going to happen)) to users ....
But at least we have one good thing - quick passing away of older parts by Intel - they simply not supply them in quantities 😀
So Apple at least [usually] forced to adopt updated CPUs. (all going for the same prices as they were in October'08)