I would wait and get use to the car with the JB4/Intercooler/Downpipes before chasing more BHP with meth. I'm actually running on my car on the most conservative power map (map 1 on the JB4), with the more aggressive maps I find the car almost too quick for public roads, but than again I dont have any access to a M3/M5
If you have access to the funds get Brids BWM to fit a LSD, it really does help the car get all the extra BHP onto the road
If your really worried about cooling AR Design also do an additional oil cooler, I asked Kevin Bird about getting one fitted but he advised not due to longterm maintanance issues..still am sure if you showed enough £££ they are not going to say no