I personally took a little less than a week between the two tests. Unlike Step 1, these two tests become much more divergent. It took me a couple days and a few hundred Uworld questions to get back into the USMLE test taking mode. I also took an NBME exam before the actual exam and it was pretty predictive of my actual score (within 3 points). The COMSAE exams however are all over the place and in my opinion are not very accurate predictors. Both years I ended scoring close to 100 points higher on the actual COMLEX than I did my COMSAE tests. Good luck to you, whatever you decide.