Currently in the market for a 6D and was wondering which lens should I buy with it? If I were to go for the body only ($1,699) instead of the 24-105 kit ($2,329), I'd be basically getting a 600$+ head start on the 70-200 f/2.8 ($1,300). These lenses would both serve as general purpose lenses but the 70-200 f/2.8 would benefit me more in my work of field (automotive photography). Also note that right now I have exactly enough for the kit. So if I decide to get the 70-200 f/2.8 I'd still need about $600-700. Thanks in advance!
Are the cars moving or stationary, how much space is around them, and how far from them will you be? I ask because I'm wondering why you think 70-200 would be more useful than 24-105. (Photographing cars isn't really my thing, but I went to an outdoor vintage car show last summer with just my 24-105 and along the way rather wished I had brought a longer zoom as well; but I ended up using the 24-105 mainly at its wide end and probably could have made do with my 17-40. The only time I wished I had a long zoom was when I wanted to do a portrait of a hood ornament with a strongly blurred background.)
But if you would prefer 70-200, and if the cars aren't moving, why not the 70-200 f/4 IS or 70-300L? They cost around the same as the 70-200 you mention but have IS, which is almost always useful. Both they and the 24-105 work really well on my 6D in even very low light (I've never experienced even a hint of the "struggling" another poster referred to).