You'll be fine with an auto, mate. (If you are ok with an auto that is.)
Drive both first to work out which one you want. Don't choose one over the other on how 'tunable' you've been told it is. Both can be tuned to beat just about aything else you're likely to come up against on the road, so why worry.
A stock auto box is apparently good for close to 600bhp, but at that sort of level you'll be VERY close to the limit and you'll stand a good chance of breaking it sooner or later. If 450bhp(at the fly) is roughly the area you're aiming at, it'll take it all day long.