Searched and did not find a good answer to this question. Wondering what you all recommend I use for a street car that will see some circuit track use in Virginia, with summer ambient temps near 100, winter near 30 degF? Car is 4.6L, 3v, 2007 Mustang GT, with CAI and 93 oct tune, about 300 rwhp, 28K miles. OEM calls for 5w20. Have read that is for CAFE and 5w30 syn is better for reliabilty in winter, maybe 10w40 in summer. Am concerned with reliabilty, both from wear during start/warmup, and running at the track in the heat all day. I plan to start getting UOA after next OC.