Your GMATPrep scores are quite impressive, but did you take them under test conditions? In other words, did you finish the exam under timed constraints and include the AWA? If so, then your scores a reasonable indicator of your future performance on the actual test. Beyond the GMATPrep software, outside company CAT's are less reliable. Usually
MGMAT comes in at second place. As for the others (Princeton, Kaplan, Knewton, etc.), I'm not sure.
But 610 and 620 seem a bit low, especially once we compare these scores to your GMATPrep numbers. When did you take these?