Why are you taking so many practice exams? CAT exams are really good for (a) figuring out where you're scoring right now, (b) practicing stamina, and (c) analyzing your strengths and weaknesses. The actual act of just taking the exam is NOT so useful for improving. It's what you do with the test results / between tests that helps you to improve.
I'll use an analogy I've used before. When Roger Federer and Andy Roddick played the Wimbledon final last week-end, they didn't learn a lot while they were in the act of playing that match. Instead, they were using everything they'd learned (and then some!)
before they came into that match. Afterward, I'm sure they've been picking apart and analyzing the match to learn more things, so that the next time they play a match in that kind of situation, they're better prepared.
The final match = taking the GMAT (even a practice test). You don't learn so much
while doing it. Instead, you employ what you learned before, and (if you're smart!) you analyze it after to figure out what else you need to learn before you take it again.
So don't just take a bunch of practice tests. Do
substantial work between tests so that you can actually improve! I really can't think of a circumstance in which it would be wise to take a test more than once a week - and, even then, I tell my students to do that only during the last two weeks before the real test. Earlier than that, it should be more like once every 2-3 weeks.
You can still take both GMATPrep and MGMAT CATs as long as you follow a few guidelines to minimize the chance of artificially inflating your score via question repeats. First, anytime you see a problem that you remember (and this means: I know the answer or I'm pretty sure I remember the answer, not just "hmm, this looks familiar..."), immediately look at the timer and make yourself sit there for the full length of time for that question type. This way, you don't artificially give yourself more time than you should have. Second, think about whether you got this problem right the last time. If you did, get it right again this time. If you didn't, get it wrong again. If you *completely honestly* think that you would get it right this time around if it were a new question (even though you got it wrong last time) because you've studied that area and improved, then get it right this time.
In terms of other sources for practice tests, unfortunately, I haven't done a bunch of practice tests from other sources myself in order to see what else is good out there - so, for this one, I'm afraid you'll have to rely on your fellow students. You may want to ask this question over at Beat the GMAT (
www.beatthegmat.com), as people here tend to be a bit more focused on MGMAT materials.
mazhar: we love it when our students recommend things they think can help other students, so thanks for your input! We do draw the line when someone from a company comes on here pretending to be a student and promoting their stuff. But when legitimate students recommend stuff, even if it's not our stuff, we like that!