If a 05 UK STI PPP with remap can make 330bhp then what are the best solutions for upgrading up to a reliable and legal 360bhp, whilst allowing for a further upgrade to circa 400bhp – also without any increase in low-end turbo lag ... and how much would it cost?

 

You're at the stage where a jump from an easily obtained 330 to knocking 400 will cost fairly serious dosh!
Turbo, injectors, fatter exhaust, re-map etc. You could be looking at £3k?
I'd love to go from my present 340ish to 380-390 but for road use, the jump is not good value?
JohnD