can i just say.. AT&T SGSIII is prob coming out June 20th. thats in like 2 weeks, itll take you that long to get an impossible to find SGSIII imported in. so youre not gonna be getting it any faster ordering it from uk.
as far as bloat.. you can remove it yourself once youre rooted, and there will be custom roms that do it for you..
as for the quadcore, the dualcore AT&T is using is just as fast, and clocked higher, so no noticeable performance differences there.
AT&T's SGSIII will have 2GB of ram, instead of 1GB.
and we just got LTE here in cleveland on AT&T.. im getting over 50kbps dl speeds.. thats not a typo, FIFTY!!! with the international version, youre looking at 4-6kbps MAX
the SGSIII on AT&T will be considerably less, (think 400 dollars less with contract).
these are all things you want to consider before getting the international version. its true in the past importing was always the best way to go, but this year seems like it may be different. id really suggest holding out a few days and seeing what AT&T's official moch up looks like