I did one PR CAT... the math was very easy (I got a 50 or 51) and I finished with 10 minutes to spare. The verbal was hard, not because it was complicated, but because the logic they used for the answer was very different from the ones that OG uses. It was the lowest I ever scored on verbal for all tests.
So take the MGMAT if you can. Even though the math is uber-hard, the scoring is somewhat representative and you'll learn how to do math tricks faster. Add 2-4 pts to your MGMAT math score and you should get what your GMAT math will be. The verbal was pretty dead on.