I don't track my car, but I swear by Royal Purple, which Pep Boys carries (on west coast, at least). It is less than a buck per qt more that Mobil 1, and the engine runs noticeably smoother with it.
07 Exige S 265: GG, Track Pack, V1, RV Camera, S111 CF roof and splitter, 4.5-lb Voltphreaks battery, 10-lb Von Hep Exhaust, Green filter, 265 crank hp +/-, Volk TE 37 Wheels, RTDbrace, Scroth 6-point ASM harnesses, Innovative Motor Mounts, Saiku Michi Catch Cans. To come: IC fans, headers, and sport cat. 1955 lbs total weight (est w/tank half full)
05 Elise: Storm Titanium, Sport, Touring, Stage II (SOLD) (May '05 - Sept '06)