I honestly wouldn't mind suffering a few tenths a lap just to make everything fair and fun for all.
And I don't think that much is needed, TDRT was able to stay up with the XRR last season. XRR 10, and FZR 25, should be alittle more accurate (totally random guess and you could be spot on).
All I know is I don't want to see one car dominating again, the beginning of last season was actually really competitive for all cars, and then the new patch came out, balancing thrown out, and it all disappeared.
i'm personaly not too bothered with having the FXR brought in to the battle a bit. As long as it is still not as competitive as the XRR and FZR but compettitve enough on circuits like BL1 or SO4.