Get the SP-01. It will get you started shooting shooter, and that's the most important part. It's not worth waiting for the S2 to hit our roster. At this point it's not uncommon for DOJ to not add a gun to the roster, even after it passes all the roster requirements. When the S2 is finally on our roster, you can always pick that up and sell your SP-01.
You can make your SP-01 very close, somethings even better, than a S2. But there are some S2 features that you won't be able to replicate. I have both a factory stock S2 and SP-01 with the CGW full production kit. (S2 was my main gun for 2.5yrs of USPSA & TTG). The CGW kit will get you a better trigger than the S2. When I compare the two, the SP-01 feels very slightly more polished; cleaner break and reset. What the S2 does that the SP-01 doesn't, lies in the S2's frame. S2 is a lot heavier in the front end. Also, it comes with a trigger guard undercut that has a very nice relief for your middle finger.