Since I'm sure that you've learned all the core concepts that you're going to learn by now, my suggestion would be to relax, but to continue to practice by doing several of the harder problems in the OG everyday, just to keep in practice. Also, if you haven't already, you might want to practice doing a few of the AWA essays. That seems to be an area that a lot of people overlook or ignore in preparation.
Also, I did my last GMATPrep CAT two days before the test. That way, I could fine tune my timing, but not be burnt out on it because I did it too close to test day. On the day of the test (I was lucky because my test wasn't until the evening on a Saturday, so I had all day), I got up, ate breakfast, went over the core concepts for both quant. and verbal (the different equations, triangles, grammatical rules, etc.) and then took a break for a few hours. Then, before I went to the test center I did a few quant. and verbal problems just to get warmed up and into the mind-set.
Good luck on test day!