Ive ran 1.3 with a daughterboard, was RR checked, fuelling was ok, inj duty at 97% and 332bhp - id say that's as much as you'll get!
bear in mind you'll prob need an uprated clutch to run that much boost not to mention an uprated fuel pump. I was using an electronic boost controller, no spikes with it. When youre running higher boost there is also a chance of leaks - check all your intercooler hoses are on tight and if possible get the clips changed to mikolor