There are a few people who have blown their motor running 8K. The stock oil pump can't handle the stress. You can upgrade to the Nismo oil pump if you really need to run 8K.
I can say this from experience, I set my fuel and throttle cut to 7800 and I watched it bounce off of 8K on a quick run. If the engine can overrun like that, then I can only imagine that setting it to 8K would put the overrun at a dangerous level.
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