Thanks again for your comparison Jamison.
Just a word of caution to the XT owners out there considering the Tamron 28-75 - Jamison's shots were taken with a 20D. My experience with that lens on my XT was much more hit or miss. In fact, at f2.8-4.5 in the 28-55mm range the lens is very, very soft. Unusable in my opinion. I sent the lens back to Tamron and even after re-calibration, it was the same. I just found out today they are authorizing a refund to me because they acknowledge the problem. And in fact, there are lengthy threads on the XT/350D/300D dpreview forum of many other XT users having identical problems with this lens. The problem seems to be limited to the XT since I don't recall any original Rebel 300d people having issues.
Also - re: the Canon 50mm 1.8 II - IMHO this is really an f4 lens since in my experience anything below that is soft (esp. at f1.8-3.5) and I have seen many other posts confirming this. For $69 it's still a good lens but don't think you'll be getting sharp shots at f1.8.