Taking PGRE 3 Times?

I have taken the PGRE twice already. The first time I really didn't study, and I got a 640. The second time I studied a bunch but went WAY to slow, so even though I barely got any wrong I didn't answer nearly enough questions and only got a 650. I have been practicing going quickly through the problems, and am trying to decide whether it is worth it to take the exam a 3rd time. Thoughts? How much better would I have to do to make it worth it? The rest of my application is very strong, this is really my only sticking point.

I say take it again, until you're satisfied that you've done your best. And practice working problems in a stressful, timed, environment.

I don't see any down side to taking that test 3 times. Toefl is quite different from PGRE but both are test for graduate school and I know some of international students take it 3 to 4 times to get a satisfactory score.