I picked up an RCF carbon a few weeks ago. Even though, it weighs 4000 lbs, it is the most enjoyable car I have ever driven as most of it went towards Frankenstein chassis rigidity with the IS-C chassis center. Before I got the RCF, for 2 years I had read and dreaded the weight as it had been so talked about in the media. Having now the car for 3 weeks and coming from a 2650 lbs 190 HP compact sporty car, I was shocked to realize it does not feel heavy at all as it shrinks around the driver when pushed hard. It feels wide in the back, but still light on its feet. I simply played with the tire pressure to eliminate tire roll and squat. After several trial and errors, 37 psi rear and 36 psi stiffens the tire walls enough to eliminate any tire roll. The chassis rigidity, suspension tuning and the mass near the center, does not make this car feel heavy at all. There is almost zero understeer even cornering at full throttle with TVD in track mode. Again, going by "feel". I have driven the E90 M3 (was on my short list along side the RCF), ISF, IS350, SLK55 AMG and the older 450 HP 2010 c63. Of all of these cars, RCF feels the quickest especially around turns with the howling sound track and the tail easily comes around if either it is slightly cold or you keep the throttle nailed through the corner.
The easiest and most obvious way to make it an M4 or C63S killer is to put big turbochargers on the engine. Personally, it was never about tenths as it was either N/A high-revving V8 or nothing, even if it was not the quickest car in the class. That is why it boiled down to either E90 M3 sedan or RCF. In the end, I chose to go with RCF because overall it was the much superior car.