My car made 425.6 bhp on a T34/63 turbo but it only lasted about 1500 miles over 8 months before the turbo needed to be replaced as at that power its pushed to its limit.

engine mods were standard bottom end with just pockets in the pistons, ported head and BD16 inlet cam. Standalone management system, hart inlet plenum and a good intercooler. 1050cc injectors

i wouldnt worry to much about the numbers and focus on the drivability as a well set up 350bhp will leave a badly set up 400bhp car standing if you can use all the power through the Rev range.