In all honesty they're good off road too. If i could find the go pro footage of the 4x4 course i was on in NZ with them you would be shocked what they can do even on the 21 inch road wheels. We were all shocked that is for sure.
I towed Kens AW11 up to MR2TC 2012 in a petrol 3l (190kw) version and fully laden, AC flat out, on cruise control we sat on 110kph speed limit all the way (only had to go down one gear) the diesel you would not even shift down.
Towing your race car you probably would not even feel the load out back at all.