300-350 what? Engine hp or wheel kw?
Lower psi means bigger turbo to make power = worse driving experience. Building everything to an exact goal is what you want. Choose your power figure, choose your block type, select your maximum boost level to suit the block, select the turbo that will deliver that power at that psi, choose your pistons rods studs bolts etc to match, choose your cams and heads to get the most out of it, and you will have the best reliable drivable power
The other approach is to assemble a couple of bits because you got a good deal, then try and put it all together around that, and hope that it works. I don\'t suggest that way!