As you increase boost pressure the turbo become less efficient so the intake charge becomes hotter. The fuel pump tops out at about 135BHP I think on the earlier engines so you'll not get any more boost that the amount of fuel the pump can supply.
ETV is right, the vp37 and vp21 pumps have a maximum rating of 25-30Kw per cylinder which totals out around 135bhp.
What you'l need is a good mix of both air and fuel, so what i'd do, rather than try and hit a particular psi - id keep the remap and fuelling constant, and slowly take the turbo up and see if she gives black smoke, black smoke is semiburnt diesel which typically suggests not enough air to complete combustion.
remeber looking through turbo charts and graphs, and throught that around 20 psi would give the largest spread of air flow for revs, but as we dont really have lag problems, can run the max which was around 21-22psi. The stage 1 hybrids are told to be able to run 25-26, with the stage 2 being the same as they have the same bearings. Running around 21 psi may cause long term damage to the charger, but no one has proved it yet, but i do remember donny putting pics up of his old turbo, with cracks in the flanges etc. and i have just found out that my old standard turbo (which has been converted to a stage 2 hybrid) was also damaged on the exhaust side. I ran the std turbo around 22 psi for about 6-7 months so there could be probelms long term.