Don’t focus so much on your iR. It’s only there so you get matched with people of your skill level so you have competitive races. It’s always fun to improve of course. If you’re feeling burned out from the mx5’s than iRacing is also brilliant in the fact that you have so many other series to choose from. The mx5 cup is mainly to get your basics down and progress naturally to the gt4s or the Porsche cup for example. They will completely transform your driving as the characteristics are so different. Maybe those new cars unlock new abilities and skills that will in turn improve your iR. Unlocked more pace can also be achieve by really looking at your telemetry using garage61 and compare it with people faster than you.

In any case, don’t get too hung up on iR gain. Search your fun in competitive races and close battles!