As a n00b I like the idea of the 4 grades... The bracket between 1:40-1:50 sounds like a small 10second difference but in reality those are the tougher 10secs for most riders. I've only done 2 races meetings and only one of them was with MA... and I'd be thrown straight into B group next year according to your suggestion. Sure, you could say I'd be given 2 more races in the Novice group but I'd still be skipping C and if you like finishing first let me tell right now, I just kissed that chance goodbye if I have to ride in the B grade described above.

To me, 4 grades gives a lot more motivation to race than finishing first in one of the 3 races you'd be allowed in Novice. IMHO, there should be both... Novice for 3 races and then automatically grade you according to your lap times/speed. My suggestion for brackets would be (and this is for 600s I'd like to clarify):

D grade: 1:58+
C grade: 1:47 to 1:57
B grade: 1:40 to 1:46
A grade: sub 1:40.

And you'd have to have more than 5 laps on a bracket before you get bumped. Otherwise you get one lucky lap following a faster rider during qually and next thing you know you've changed grades.