If that rear wing is not for visuals, it will greatly increase drag. The goal of any serious racer is downforce, not speed.
Drag = rhoACD*V^2
If the S7 TT reaches 230 mph with 750 hp, then it has a .33 CD, for the S7 C to reach 230 mph, it will have a CD of .44. If the S7 C maxes out at 250 mph, its CD must be .343, which is barely more than the S7 TT.
For comparison, the CD for the Viper and Viper ACR [using my estimates] are .39 vs .55
There is no such thing as fast enough. lol. Especially as suspension and aero technology increases.