Apologies if this is covered in another forum but I can’t find anything on the subject.

I currently have a mk2 fabia 1.9tdi (pd105 bsw) and I’m looking at tuning it up a bit I have pd150 injectors ready to go in a and a big FMIC and supporting mods will be done to cope, the main thing is obviously the turbo I need to upgrade it to get anywhere near the power I want but don’t want to pay twice, my idea being rather than getting a turbo that’s rated for 200-250bhp could I get a turbo that’s rated for 300-350bhp and run it at a lower bhp until I’m wanting to go for those higher figures to save me buying twice? 

A big turbo means horrible lag, especially when under utilised. That said, shooting for huge numbers is a terrible idea if you want a reliable car, 220 BHP is the sweet spot in terms of bang for your buck on a PD, bear that in mind if you're watching the pennies.