You've made some very nice progress so far.
Assuming that you took the practice tests under 100% official conditions (including essays), and assuming the 670 is your most recent exam, it looks like you're in the high-600 to 700 range right now. If you really want to go for the 730, you shouldn't take the test in 3 days - you need to get your score up into that range on practice tests (taken under 100% official conditions) before the real thing. If you had said 680, 720, 720 (under official conditions), then I'd say go for it. But not with a 670 as the last score.
If you would love to have a 730, but your "I want at least this" goal score is in line with your most recent score, then you can go ahead and take the test. Just don't have high expectations for that 730. :) You should not expect that you are going to get better between your last practice test and the real thing - mostly, the last practice test is fairly reflective of the real test, especially if the practice test conditions mimicked real conditions as much as possible.
Next, the general rule is that we do less as we get closer to the test. The final day should be no more than 2h max of high-level review only. Taking the Quest for 750 workshop 2 days before your real test is sub-optimal; you won't have time to practice and really internalize the material. You also risk tiring your brain out right before the real thing. Unless you're already at a really high level with quant, and the workshop will be like "brain candy" for you, I'd be wary about doing that so close to the test.
DO NOT take a practice CAT within 3 days of the real test. (For my own students, the rule is 5 days - I'm even more conservative than the company on this issue.) I cannot stress this strongly enough. You will not get any positives out of it and you risk (a) lowering your confidence if you don't like your practice score, and (b) tiring yourself out right before the real test.
You may want to take a look at the below pair of articles; they take about what to do for the last 2 weeks before the test. Obviously, you're only a few days out, but you can follow the advice for the last few days.
http://www.beatthegmat.com/mba/2010/08/ ... -game-planhttp://www.beatthegmat.com/mba/2010/08/ ... -to-reviewLet us know what you decide to do. If you decide to postpone and want to talk about what to do in order to try to get your practice scores up more consistently in the 730 range, we can help!