I'll sometimes do a M35+ crit before a Cat 4 crit. I'm killing myself to hang on to the 35+'s as they are quite fast. But, even when I do finish I don't find I lack for anything in the Cat 4 race. If anything, I'm less uptight and more relaxed mentality and physically for the second race...if I happened to do well in the M35+ race then my confidence is high; the pre-race jitters are gone; and for whatever reason I'm more willing to take some chances feeling like I've got nothing to lose. If the Cat 4 race is my only race then I'm more worried about "making it count," thus I tend to be more conservative. F'ed up, I know.