The TD04 in the Bug WRX gives barely any lag but at a loss of top end - 212BHP std. With the addition af a de-cat/sports cat and Air filter plus remap you should be looking at around the 270BHP mark with 1.25 Bar boost (max) coming in by 3250rpm 1 Bar at around 3000rpm.
Swap the TD04 for a VF34 and you're looking at around 330BHP (assuming you do the injectors, fuel pump and intercooler as well) go to a TD05-18G and you should be in the 350/60s which is about as far as it's reccomended to go on a std Bug wrx gearbox and internals. I know loads will say 'I've got more and it hasn't broken', they always forget to mention the yet! Of course you may be fine with more!