the 18 - 55 II lens is much better than the version I
the 55 - 250 II lens (just introduced) is better than the version I in image quality
as far as I know the new and the old versions of both lenses are pretty much the same, there are only some cosmetic changes, so it really puzzles me why you claim that the version II of the 18-55 is "much better"
I'm not sure what the numbers are but it has been pretty well established that the newer 18-55 is much better than the one that was included during the XTi era, in sharpness, contrast, build quality, and of course the introduction of IS.
Technically speaking, there have been something like 4 different iterations of this lens - the original one that came with the 300D-XTi (possibly XSi), then the 18-55 II, then the 18-55 IS, and I believe there's been minor revisions to one of those as well. The main difference optically, though, is between the original and the more modern-looking ones.