Vietnamese site Tinhte, which has past form on these kind of things, has got its hands on the GT-I9300 -- purportedly the Galaxy S III if Samsung decides to follow its own naming convention.
As we said, the main differences you'll see between these US-centric models and the original version are the processor and amount of RAM used: the American variants all make use of a dual-core, 1.5GHz Snapdragon S4 chip and 2GB of memory, while the I9300 runs on quad-core Exynos silicon and one gig of RAM.