Should drive nicer and be more responsive but probably no more power at the same boost level....the power you have at 18psi is very good and as said i can't see you getting a genuine 270bhp whatever boost you run with that turbo. I too will find out as my old engine was running similar power at 1.5 bar on a hybrid t3 so when i get it mapped again i'll find out if it's worth running 2bar, though i'm doubtful as to whether it'll make any more power just torque. What form of efi are you going for mate?