///Audience
Ready to race!
I found an excellent priced k04 but the owner was running the GAIC extreme file on it. Is this a major red flag? The turbo appears to be in excellent shape cosmetically.
From reading Giac extreme file website. It looks like they run the turbo a little harder in the surge zone than some, but peak airflow is about the same as APRs. So they make their extra power by timing since they are using 104 octane + w/m for the extreme.
I'd not worry about it being worse for the turbo than other tunes. Remember, turbo wear is about how much surge it sees, operating temps, how hard it's run, oil change intervals, etc.
Personally other than harder in the surge zone it should be fine.