Wow, what a blast. I just got back from California Speedway this weekend (running the infield road course), but not with the 914 - my Dad and I rented Caterham 7s.
http://www.caterham.co.uk/showroom/index.htm
I've always liked 7s, and have toyed with the idea of getting one (probably to replace the 356 [my ~2000 mi/year car]), but had never driven one. The 7 certainly makes a not-so-good driver (me) look very good! My Dad and I were the only 7s and we were always 1-2 in our group, which included a 996TT, Viper, 83 Euro 930, C5s, an M3, A4, spec Miata. Many of these were dedicated track vehicles.
Ours had 208 HP Ford Duratec engines (new Ford Focus), and were 1250 lbs (wet, no driver). 0-60 in 3.8 seconds, and crazy handling.
Impressions: the Caterham is a no compromise vehicle. Performance is the only thing it does, but it does it very well (but they are still street legal). In comparison, the 914 is a comfortable, quiet, fast, heavy GT ride.
Attached is a not so great picture, but you get the idea. Anyways, off topic, but thought some of you may be interested. As ours were configured, they are about $38k new. The rental service we used was: http://www.autocourseinc.com/