The 70-200 f4L should be grand for r/c car shots. I've got one and its my most used lens for rallys and other things.
I coupled it with a 17-40 f4L too which was great and ultra sharp, I had to sell it due to lack of funds at christmas though
I dont know much about the EF-s lenses but im sure somebody will have more experience than me on those. The 17-55 f2.8 IS has always been held in high reguard by most people i've talked too who owns one, i've no idea on the price of it though.
Currently I have 10-20mm then a huge gap till 50mm, im looking to fill it either with the canon 24-70 f2.8L or the sigma 24-70 f2.8 if I cant get the funding for the L glass.