hi there,
it depends on what you would define as laggy?
if you're looking for the same response as the factory turbo, then this would be laggy for you.
re: full-boost, etc, like i wrote previously, this setup was on the car when it had an RB24DET (stroked RB20) before i bought it so i'm not sure when full boost came in exactly b/c i didn't get to drive it.
although, i was taken for a drive as a passenger and with the RB24, it didn't feel laggy, and it was only on 10psi.
fyi, the RB25DET NEO is a good flowing engine and it will run this turbo perfectly.