I had the opportunity to drive a GT3RS 3.8 (2011) on the track and found it much more difficult to drive than my E90 M3, E46 M3, S2K, or Spec Miata. The gearbox is tough to work without actually owning the car and using it on a daily basis. The brakes are incredible and the grip is great. However, it does require some seat time to get used to.
I have a few hundred trackdays and have set pole/won races. I was unprepared to drive the GT3 beyond 7/10ths. In 12 laps I got within ~8 seconds of where the car could be on Thunderhill driven all out. I would need more time to get used to it. The RS 4.0 owner may be just new to the car. Comparatively, in 2 sessions, I was within 2 seconds of Randy Pobst's time at Laguna Seca in my 100% stock E90 M3 (tires & pads stock, too).
I's just a harder car to drive with higher limits and a balance that isn't as intuitive. Once mastered, I'm sure it's incredibly rewarding because it was even a blast to putt putt around in 4th gear all the way around the track because we were still pulling laps faster than anything I have ever driven before that.