If you are only there for 4 weeks then I would get the exams out of the way before you go over there. Its not impossible to pass them once over in the US but when I was over there students were locking themselves in their rooms at night and not actually enjoying being in CA. I took all my exams in the UK and then just did the R/T exam in the US as the guy I used was licenced to conduct it.
Yes you may find it a bit more confusing to start with 11 weeks you shouldnt really have a problem. Once you start flying you will build on your knowledge anyway and it will be etched into your memory, the important details anyway!
Get them done now and then all you will have to concentrate on once you get there is keeping the aircraft in the air and passing the flight test.