Buy the tools (cheap) and do a compression and leak down test at intervals. Takes about 30 minutes if you have practice. This will be your answer, everything else is speculation. It's worth nothing that it is not unusual for degradation to occur quickly, not necessarily in a linear fashion as we'd prefer.
At least one individual, a guy I know in Houston, ran a basically stock s2k motor at 580-590 whp for nearly 3 years. He used the power fairly regularly as well. He started losing compression in I believe cylinder #3, took off his turbo kit, and still daily drove the car for two more years before selling it. 600whp is 800whp on the NSX motor by displacement, but the engines are obviously of different configuration/internals. The key in his mind was frequent and professional tuning. He spent about 2500 annually making sure the tune was exactly where it should have been. On a less custom/complex setup it would be a fraction of that cost.
