A decent 3" exhaust with downpipe and sport cat coupled with a decent filter and intercooler will close on 300 with a decent map.
We are running a 2010 ST3 with only a dreamscience map on it and thats at 263 at the moment. Once its out of warranty I have a full 3" Mongoose system and Airtec intercooler to go on it, unsure of the filter yet though.
Good little cars, sound ace and handle well. The missus uses ours around the doors and averages 19 to the gallon!!!!