Power has (almost) nothing to do with what you can run at the wheels. Its all about how good the tune is. You might get 250atw with a td04 on stock internals but its the tune that determines how long your engine will last.
it can and will last with 230whp ---maybe more ....but its more to do with the tune....its been by several people already for ages------on standard internals
i've seen 200-250whp on oem intermals..........still running strong
and more has been recorded
but i know what u are saying turbodave...as everyone cant achive this....your tuner must know what they are doing....and the engine must be in good nick
its not necessarily what tune u ask for.....but u will realise those who run a fair amount of power through stock internal for a long time......normally have a tuner who might be a bit familiar with the 4e/5e engine AND/OR has considerable experience of tuning so they know what works and what does not work
things like this is an art and not necessarily a science