I would probably lean more toward keeping it a 27T/17.5 class just to keep the speeds down. I agree with charlie_b that cars will handle so much better, and last longer, if we can limit the power.
Another thing we have to keep in mind is that both charlie and I are partial to parking lot tracks, and there usually isn't enough real estate available, to set up big tracks, so stockers will be more than we ever need in these situations.
As far as newbies, we can always set up a "RCGT Sport" (or GT-1, GT-2, whatever we call it) class, just to give the brand new guys a place to race while they get the hang of organized racing.
We can also run RCGT and RCGT Sport together, and score them seperately if there isn't enough of either class.
People who would be eligible for the newbie class would be at the discretion of the class directors...