Seat position is key, and at 6’2″ you may find it difficult to get the proper seat positioning. Do you have an extended front porch on the kart?
Generally, I’d would think that with proper seat position an S25 axle on a low grip track with medium tires (YKC or mogos) would not be stiff enough.
What size front spindles are on the ’05 RR, 17mm? (For reference the newer models are 25mm)
Fundamentally, Due to the ‘low grip nature of the track’ you run the kart chassis looser (i.e. a 30mm chassis is better in low grip, 32mm chassis is better in high grip), but due to your height/weight you would run the chassis stiffer (high CoG puts more load through the chassis).