As always with a Caterham, it's an awful lot of cash for what it is, of course. £50k for a seven is really ludicrous, IMHO. If the price tag was closer to the Atom's, (and I don't see why it shouldn't be) it would be a fairer comparison, but I wouldn't mind betting the Atom's chassis is much better able to use that amount of grunt. In terms of touring, you have to regard an Atom as a bike. Waterproofs, helmet, no luggage. A seven is a little more civilised, but still expect to get very wet if it rains properly.
Alternatively, get yourself a 2nd hand seven, drop perhaps 5k on a sexy sequential box and probably the same again building a supercharged Duratec (less if you're handy)...
Not even sure I'd want a sequential box for road use.. or 310 BHP, frankly. There are some roads where you can never have enough power. On most roads, my 200 BHP offers enough potential for near-death experiences in a car 100kg heavier. So.. we're back to it being a track toy, in which case the Atom would most probably win hands-down.