I think you'll be closer to 250bhp for a newage wrx with the PPP. They very rarely made near the 265bhp Prodrive claimed when rolling roaded.
If you need it to be MOT friendly, then you will need to keep a cat in the downpipe. Try and pick up a decent sports cat downpipe and then with VF35/pinks etc and a remap you should see 320ish.
Not seen the toyosports uppipe but if its got a larger internal diameter than standard then i'd put it back on ebay and get a genuine STI one or a harvey uppipe from Alyn. Bigger is not better with uppipes
