There are a couple of threads dealing with this general subject. Several members are recommending Rotella Synthetic. Others are saying Schaeffers. Currently, GC has been referred to as a thick 30, 12.1cst @ 100. RTS is listed as 14.6 @ 100, a true 40 weight. Schaeffer Supreme 7k is 10-12cst @ 100 as listed on their site, and the full synthetic Supreme 9k is 13.5 to 14.5 cst @100. I don't think it is a question of if I will switch, only when. When I do, I'm fairly certain Schaeffer will be in my radar, based on what I've read here, and the company reputation. Giving up the exotic esters in GC will probably be as hard as breaking a 500 dollar a day crack habit though.