Track day car ...what to get

[gra001]

Just finished doing bike track days and now going to move to cars. Have been looking at mainly Caterham and Lotus because was going to use on road as well. Now thinking track day use is the main objective as road doesn`t seem to hold much excitement after the track. So, Radical, Atom, Lotus track car now in the mix as well. If Radical......SR3 or SR4? Any help/ideas appreciated.