Using the old MKII street car as a way of comparing how quick a modern IRS challenge car would be to any other car is apples to oranges. The newer cars have better suspension setup on all four corners, plus the chassis in the challenge cars is a good bit stiffer. I don't have any experience driving an Excocet and have never heard bad things about them, but I wouldn't say they are as quick as a properly setup challenge car from what I have seen. My experience is being at VIR with them for UTCC and some other NASA events, at no point were they quicker than us.