Where to find difficult quant questions?

I just started studying for the GMAT, which I am taking in two weeks. I downloaded the GMATPrep software and today took the first practice test.

My score was a 760, which I was pretty happy with. Raw scores were 49 for quant, and 46 for verbal.

I'm not too worried about the verbal, as I had plenty of time (25 minutes leftover when I finished), but the math was excruciating.

Unfortunately, most of the prep problems that I have looked at so far fail to mirror the difficulty of the quantitative section. I knew I was getting the problems most correct, but it was taking me so long to work through them that I was seriously risking running out of time. Where is a good resource for finding the most difficult GMAT math problems? I want to practice at a high level so that I am better prepared to pace myself when the real test comes.

Any other tips for what I can do to maintain or raise this score?