Hey Roggers,
First of all.. the RSR Porsche is NOT an MR but an RR. Unfortunately, I personally don't like the Porsche at all. Before 1.13 the car was really great for my taste. It drives very well balanced without too much oversteer or understeer... but now it is the epitome of understeer in general, how other drivers can achieve even halfway good lap times with it is a mystery to me, they probably force the car very hard, which is what it is does not suit my driving style.
If you want to drive an MR that is really very good, is also fast and can also save fuel relatively easily... test the Ford GT LM Spec II RaceCar, of all MRs I think it is the most good-natured and at the same time still fast enough in order to be able to cause surprises on the track.