I still recommend that you save your a bit more money and jump to a Cayman S, which is a much better track car with the fixed roof. Some minor upgrades to the exhaust/headers and suspension will have you in very good shape. 300+ HP with lots of balance.
I was at a DE event last month and it was obvious the Caymans were performing very well at the track, even with novice drivers.
You can get a low mileage Cayman S around $50K, would think they will start dropping into the 40's soon.
http://www.autotrader.com/fyc/vdp.jsp?car_id=213229822&dealer_id=58999983&car_year=2006&num_records=25&search_type=both&make=POR&keywordsfyc=&distance=0&transmission=&model=CAYMAN&make2=&address=55337&default_sort=priceDESC&certified=&advanced=&max_mileage=&max_price=&sort_type=priceDESC&min_price=&first_record=226&body_code=0&end_year=2008&color=&keywordsrep=&start_year=1981&drive=&pager.offset=225&engine=&style_flag=1&doors=&fuel=&cardist=1021