I think you can expect to work more hours as a surgical intern vs. a medicine intern.
However, when I was an IM intern I only had one non-call month (one outpatient medicine clinic month). All the rest of the months it was Q3 and Q4 in house overnight call, admitting patients all night. But in general the daily hours are longer in surgery because you have to get there even earlier in the a.m. And you probably won't get to see the OR much, if at all, so you have to think about what you'll be getting out of it all, educationally speaking.
I think if you enjoy surgical rotations more, you can do a surgical prelim year, but just realize that you are going to work more. If trying to interview @the same time for advanced positions (b/c didn't get a categorical spot first try) it might be really, really hard, or impossible. Of course it would be hard if doing an IM internship as well.
What specialty or specialties are your ultimate career goal? If not something surgical, then I'm not sure doing a surgical prelim year is going to help you a lot...IM can be used as PGY1 for more specialties I think (i.e. neurology and some others that surgery prelim years can't be used for). On the other hand, sometimes there are surgical prelim spots that IMGs get at some pretty decent academic hospitals (i.e. Dartmouth, Vanderbilt, U Texas system, etc.) because surgery programs always need prelims. Just don't expect to get to stay there as an upper level, though, as a lot of places take a lot more prelims vs. the number they even intend to keep on for PGY2 and above.