I like Rick's idea... only issue I see is that there are riders out there riding different classes on the same event. So if you're a B grader on a 1000 and decide to give the 600s a go as well how would you go about getting your grade back to C?? To me, that is also the whole problem with doing the grading based on laptimes. I reckon the experience idea is a valid one... but maybe remove the rest so it doesn't over complicate things.