I'd hope the S2K is faster than an RX8 on low-budget suspension and worn-out tires, R-comp or no. The stook is lighter, more power and TQ, and on quality suspension.
At the last Apex I did, I was faster than a good driver in an Exige because his tired R-comps couldn't hold 1G, while I was getting 1.2G from RS3's.