by the time you piece together the turbo kit, you'd have spent more than the price of an S52. but if you're going to turbo it i can see how this makes sense.
Because the OP wants to race, i would suggest N/A. instant response, less parts to fail or a supercharger. the bmw motors respond well to this. i know a properly tuned and matched turbo system can have boost as low as 2500rpm or lower. however for the add'l cost. kinda seems prohibitive for only 300hp