MGMATs are pretty accurate. But you are right -- the Quant is actually a bit harder but the verbal section is spot on. MGMAT tends to "trick-up" the quant section a bit more -- but that is good practice before the real thing. I think scoring wise -- MGMAT might slightly underestimate your score -- so in reality you might be closer to 700 than 650. But for all practical purposes I would say you are in the range between 650 and 700. Also, not doing the essay section can over-estimate your score by a few points. There is a big difference between how your brain performs after 2 hours vs. after 4 hours. The sheer length of the GMAT adds to its difficulty.