I think clearly defining the problem you want to solve is the first issue. Are you simply trying to reduce the size of AA in the GP's?
It stands to reason that the GP circuit will be top heavy as no-one really wants to travel 600 miles to shoot an average score.
If you want to divide AA up, it doesn't really matter whether you add a D at the bottom or AAA at the top, but for the sake of logic and simplicity, I would personally prefer the top grade was called A regardless of which grade we then end up in.
Anschutz 2013 MEC1 .22LR
Miroku 3800 12bore