I'm a long way from any new mods - I have 6 that all need varying amounts of finishing up, I have to catch up
As for balance:
The 100 is balanced to XRG and XFG, comes out somewhere between the two.
The 200 is just above TBO, we use 5% res on DD to balance it. Rony has it in RandomCar also, but uses 80kg and no res instead to balance. (It's very light, doing it with weight instead of res lessens the tyre advantage as well as matching the speed.)
The 300 is well matched to iiiiil's COQUETTE Z5. The Z5 has slicks available and the 300 doesn't so you need to watch that, but they match well when on the same tyres. We also have the FRAUD 040 and AM PHOENIX in that class, but those are both 4-speed boxes and that's enough disadvantage for them to get eaten alive on tracks where the speed varies a lot.
The 500 is balanced to GTR class. (I say balanced but I'm pretty incompetent at driving anything involving downforce so I dare say this one probably needs some work
)
I've attached our class guide graphics for each.