Coincidentally, I did this comparison back in 2017 or so just because it is what I had available

. I had a very good track with some very fast sections and also a lot of tight twisty bits. 16 turns in all IIRC. It was mostly short grass with dirt showing in the faster turns. I ran a KF2 (mid motor with the "low grip" conversion that moved the motor back) and a re-re XLS with pro transmission but otherwise stock. Both had the same electronics and 7.5 Reedy. I wasn't trying to do a comparison; I was just running them as hard as I could, making tire and setup changes for the best lap time. It was great fun. I had the Laptrax timing app on an old phone with a bluetooth speaker calling out my lap times.
After hundreds of laps with both cars, the XLS was consistently faster, but only by a few tenths of a second. My fastest laps were in the high 28s for the XLS. I can't remember if I got the KF2 into the 28s or just very low 29s.
A couple of takeaways:
The track was much more suited to the XLS. A British track circa 1987 would have been bumpy, grassy, not a lot of jumps, so the CAT was on home turf. The KF2 was designed for sugar or carpet.
A better driver would have gone faster with the KF2, possibly beating the XLS. I turned down the throttle EPA on the KF2 (in multiple steps) to get it under control, and then back up as I got better at driving and with setup. I eventually landed on ~85% as the limit FOR ME. A better driver would have also been faster with the XLS, but it was set to 100%, so perhaps not as much faster than me as with the KF2. He would have better skill plus more power on the KF2 vs better skill only with the XLS.
All of the suspension changes combined were nothing in comparison to the gain from swapping tires.

Even the low grip conversion (the motor and battery swap locations front to back) was less significant than tires. Everyone else probably knew this already, but I had been away for 25 years or so.
Both cars did best on the same tires. Schumacher Mini Spike 2 were the best I tried on either car.
You can see the outline of the track in this aerial real estate photo from when I sold the house.
