In general, I'm leaning towards postponing. If you need to rush through the last 8-10 questions in each section, that means your score is dropping at the end of each section (and on the GMAT, where you end is what you get). So you're knowledge level is higher - if the test weren't timed, you could perform a lot better - but your test-taking skills are pulling your score down. And it typically takes at least 4-6 weeks to fix serious timing problems.
If you just want to get in there to see what it's like, and you won't be demoralized or discouraged if you don't do well, then you can always do that. I don't generally recommend that, though, because most people will get discouraged.
You don't need to do super-well on IR. You just need to get an okay score - like the essays. Also, it's not surprising that you thought "Yuck!" on the first few IRs you tried. I thought the same thing - part of that is just because they're so unfamiliar. If you actually study for them, you'll be fine (at least to get an okay score).
Given the scores you've shown so far, I agree that you have a shot at a 700+ IF you fix the timing.
Read these two articles:http://www.manhattangmat.com/blog/index ... to-win-it/http://www.manhattangmat.com/blog/index ... anagement/
Then, use this to analyze your most recent MGMAT CATs:http://www.manhattangmat.com/blog/index ... ice-tests/
And this to help with studying going forward:http://www.manhattangmat.com/blog/index ... -the-gmat/
Next, don't take another practice test until you have made *substantial* progress on the timing. Otherwise, you'll just be wasting a practice test. Also, you can test yourself out on smaller tests first - eg, try a GMAT Focus section (www.gmatfocus.com
, quant only). Note that GMAT Focus will not cut you off at the 48-minute mark. You have to track that time limit yourself. (It will tell you, afterwards, how much time you spent on each question.)
If you'd like, come back here and share your test analysis with us, tell us what your study plan is, etc. We'd be happy to tell you what we think about your plan!