If its for tuning forget the lower capacities, you'll only be pissing into the wind trying to get to a power level you could have bought in the first place.

Just get an rs or st you'll have a better car as standard than you would if you bought a smaller one and started tuning it, plus it'll probably work out cheaper £/bhp.

Me personally, I'd be looking at the 2ltr diesel, get it remapped and it'll be nippy enough and still good on fuel.