I was going to study more LSAT questions but decided not to after reading this:
one thing to watch out for is the HUGE differences in the critical reasoning section. both of the exams have CR sections, but the content and question types are radically different.
the lsat CR section features many themes that simply don't show up on the gmat CR section. here are some examples (i don't have any lsat questions in front of me, so i'm going off four-year-old memories here):
* equivocal / differential meanings of the same term (nonexistent on the gmat)
* mimic an argument / find an argument that's structured the same way as the original argument (very rare on the gmat, very common on the lsat)
* formal logic, using contrapositives, deductive logic, etc (essentially nonexistent on the gmat)
in general, the gmat is much more focused on inductive logic - i.e., the type of logic that generalizes from observed patterns or premises, requiring additional assumptions along the way. the lsat, by contrast, is more focused on deductive logic - i.e., mathematically formal logic, from which statements can be deduced with absolute rigor, devoid of additional assumptions or empirical evidence.
if you're a very linear, logical, mathematical type of thinker, you'll probably find the verbal component of the lsat easier. if you're more of an intuitive, inductive thinker, you'll probably find the verbal component of the gmat easier.
the gmat also has MUCH longer sections without any sort of interim or break - 75 minutes apiece, compared to something like 35 minutes (i think; i don't remember exactly) for the lsat sections - so you'll also need a fair amount of additional perseverance.
