Thanks to all for the above replies. I have read the hometheaterhifi article, and it was part of the reason for my question, i.e., the Select2 was geared for small rooms, and Ultra2 for large rooms. It may very well be as suggested above, though, that Ultra2 is simply more capable and better, even for smaller rooms (though it may not be NECESSARY for them).
I suppose I should just wait until the Onkyos (805, 875)--which are rated Ultra2--and Elites (91 and 92)--which are rated Select2--have been out a while to hear how they compare with each other. Though the Onkyos look better on paper, I still have a high regard for Pioneer Elites.