I don't know if anyone is running all the challenges now but just thought I would throw some in for consideration.
Silverstone Triple Treat - Run each of the three Silverstone tracks at B(or A) class and add up the total time with the lowest being the winner. The only catch is you have to run a different car at each track and you can only have 1 FF, 1 FR and 1 of the rest (FA, RA, MA, MR, RR).
TTR3 - Running three reverse test tracks, lowest total time wins. Running A B class at Copperhead R, A class at Inland Taipan R & S Class at Death Adder R. (tracks only a suggestion)
A Class Professional - Run the whole of A class Professional with one car and one setup (excpet FD gear change allowed), again lowest total time wins.
Whatcha think? Quite happy to run any of them if you like the sounds of any?
-K