The one thing that a practice test can never really replicate (relative to the real test) is the anxiety of knowing that, this time, it counts. That anxiety can lead you to bad decisions during the test, such as spending too long on some questions and rushing on others, or in general rushing on things you consider your strengths to try to reduce the time pressure on other problems (thereby opening yourself up to careless mistakes). And so on.
Our quant tends to be harder than GMATPrep and also tends to punish you more if you have some of those bad decision-making and timing habits. We can't hypnotize you into thinking that this practice test really counts, but we can still try to set you up for some of the bad reactions you might have when you really do take the actual test...and see whether you fall for them. :)
Verbal is strong for you, so any effect wouldn't be as pronounced - but your quant performance could also bleed over into verbal, because if you, for example, spend too much mental energy on stuff that you should be letting go, then you'll be more tired when you get to verbal and make more mistakes than normal.
So, what to do. You need to dive into the data and see what's going on:
http://www.manhattanprep.com/gmat/blog/ ... ts-part-1/In terms of which is most likely to reflect the real test - I've seen people closer to ours, closer to GMATPrep, in between...it's hard to tell unfortunately.
But here's what I think: if your drop in performance on our CAT specifically reveals the below, then you'd want to get this cleared up before you take the real test.
Major Issue: Timing issues tied to decision-making / mindset. You get sucked into some questions that you really should have cut off and that impacts you elsewhere in that section or later in the test (you rush and make a mistake, you get more mentally fatigued before the test is over, etc).
--> The flip (though less common) can happen, too: you're so nervous that you start rushing, finishing early and leaving a trail of careless mistakes in your wake. But I'm writing that for others reading this, as it sounds like your issue might be the one in the previous paragraph.
Anyway, back to the "sucked in" issue. On the real test, expect to feel that same pressure / have that same tendency because you know this one counts, and a part of you is going to want to default back to the "old school get everything right" mentality. The question is whether you can successfully suppress that mentality. :)
So go back, analyze using that article, and tell me what you think is going on.