Thanks everyone! This was one of the few panning shots that turned out to my satisfaction from that race. I probably spent 2/3rds of the race doing panning shots... it is indeed difficult. I was using a monopod, but the keeper rate was definitely still low. I did get this printed, and it looks wonderful at 11x14. At full resolution you can actually read "PORSHE" on the brake calipers! Further pics from this race can be found here:
Pirelli World Challenge - Album on Imgur Next year this team is fielding a car (Porsche 911 GT3) with a professional driver in the top class (GT) in the Pirelli World Challenge, in addition to this GTC Cup 911 with a gentleman driver/team owner. They race all around the US, so you might check and see if there is a race near you:
Schedule - Pirelli World Challenge