Get it remapped 
Yep.
PM the Doc on here (although I'm sure he'll be along soon enough). From what I've heard he's had some great results on the GTD's and he seems like a decent enough guy.
From an objective point of view, a tuning box is easier to install (plug and play generally) and cheaper. So it can appear attractive. But a remap will set up your car much better. You may only see marginally improved figures with a remap (over a tuning box), but the way those figures have been achieved will be the difference. I'd err away from generic maps, but Doc installs custom remaps on cars on an individual basis, so you know the mapping has been specifically tailored to get the most out of your vehicle.
Maps are a bit more expensive, and a bit more hassle to install (because often the good tuners are a bit of a trek away) but the dividends you'll reap will be a smoother power delivery and longer life out of your engine.
Can't recommend a remap enough!
