1.2bar is the most I would go, N1's perform well at that boost , At the end of the day dyno figures don't meen much it's all about power delivery and how early on your making boost which equals good times at the track .
An example of that theory would be wrxhoons's (from these forums ) r33 GTR he's running a Power FC tuned by Ben at Bel performance , n1 turbo's at 1.2bar , catback and front pipes , everything else stock even the air box and he has gone 11.7@119mph out at WSID with 60ft times that aren't all that great . The car would also perform equally well on the roundy roundy stuff as it has a usuable power delivery .