i agree with what you have said above, everyone has there own opinions on what lag is. my opinion is based on going from a standard turbo to a hi flow and then to the gt35. i was of the opinion that it would be laggy before i bought the set up but was advised to for a drive in 1 with a gt35 set up and i was very happy with how it went so decided yeh ill do this for mine aswell. couldnt of been happier with how it turned out.
for the OP, just abit of info with my set up, we pulled 290kw atw on a standard engine with 550cc injectors, walbro fuel pump, PFC and just the usual stuff like exhaust and intercooler.
the engine was still in perfect shape aswell.