Hi mate,
While I'm not a club official, I do get to go to a few different club nights around the place and see different rules and approaches. After reading this and your other thread on the pace of trechnology, I've got to say I'm onboard with your thinking. But I have a suggestion, a cheap one which I don't think anyone else seems to have suggested.
in Karting we have spec gearing. and maybe that might be a cheap way for clubs to bring down speeds yet keep the overall spec in line with a regional/national car that would allow drivers to progress. If it works there then maybe it can be put forward in the next years EGM.
Maybe either limit the whole Production Cup or just your F3's(or equivilent) and call it something snappy PC(25:70) or F3(22/68) - gear as appropriate. Yes you still have the roll out difference in the tyres but its still a simple and cheap (just over a tenner) way of controlling speeds even of a 13.5t. Then by the time someone feels brave enough to go off to a regional they'll probably be able to handle stepping up a few teeth.
To me as an outsider looking into GT12 as a second(third,fourth,fifth class
) having a full spec GT12 Super cup car 'just with a 17.5t' doesn't seem like much of beginners or entry level class, its more of an intermediate step just before Super Cup. But thats a different discussion, maybe for your other thread
p.s. I think the sport pack waiver is a great idea BTW