turbo's
 

hi ive been told i need a td05 16g turbo to get the best power gains from my uk turbo along with some other bit. just wonderded if this is right.
its had a prodive package fitted at some point if that means anything, i dont no if the engine is standard or not
can anyone help

First find out if your engine is standard .

The td05 16g is a good turbo but really it all depends on how much power you actually want as the range of turbos fitted to imprezas is quite expansive.
The car would need to be remapped as i don't think the Prodrive ecu was mapped for a td05 (may be wrong though).

td05, full decat, fuel pump and a good remap, should see you on your way to 300bhp

or a vf35/vf34 decat map etc etc for 330bhp, tbh i'd figure out what you have already and then what your budget is and then see what your options are.