i'm currently running a custom setup with a TD04 subaru forester turbo, had it on my car for almost 2 yrs, & 35,000 kms, regular servicing & hasnt ever missed a beat, stock engine internals. Engine is the L15A & car has been tracked quite regularly

Turbo Lag is not to bad, starts spooling @ 2200rpm & full around 3k. & If you do go custom i would highly recommend a aftermarket ECU, money well spent. Also i'm currently using delphi 380cc injectors which i found did the job very nicely.
If I were going to go for a off the shelf kit i would consider Top Fuel as well as HKS, but i'm unsure of the fitment for the USDM Fit's.