Has it been thrashed on the limiter for 100,000km or has it cruised in 5th gear for 100,000km?
Is there inherently anything wrong with the engine as it currently stands? Hairline cracks, excessive wear on components?
Whats its existing service history like for the entire life of the car? Not just since you've owned it.
How much boost has been run through it so far? Through what turbos? How regularly?
Has it been on the track? Regularly? In what conditions?
Even *if* you knew the answers to all those questions (and probably more too), you *still* wouldnt be able to give a definitive answer to your question, but you would be able to give a better, more informed estimate.
You wont find a definitive answer mate, people will only be able to give you an idea of what a GTR in that condition running those turbos would *typically* be able to handle