On your 170 a pdf delete and remap will take it to 210bhp
on my 2.0 TDI 140 i have had the following done:
Hybrid turbo
Stage 1 clutch and flywheel (darkside developments)
DECAT
EGR Delete
Backbox Delete
S3 Brakes
Car is doing 220 BHP...
if you wanted more power you could try any one of those and then upgrade the intercooler or injectors and get your car up to 260bhp