I've seen worse off rotors than that used in turbo 13B's with no significant problems.
Personally, I wouldn't hesitate to use that rotor (although I'm more of a 8.5:1 junkie

) in my engine - take it however you want and standard disclaimers apply here.
Good parts are just getting harder and harder to come by.
The FD is already hitting 15 years old since last production ran.
You tend to get a little looser in your standards when parts start to get harder and harder to find.
The apex seal should have enough support as long as it passes clearances spec.
The apex seal is ductile enough to handle most "normal" combustion loads.
400hp should not be a problem, as long as tuning, fuel, and ignition timing are spot on.
This is assuming at the very least Mazda OEM 2-piece apex seals or better.
Once the motor detonates, all bets are off - you might be a little bit more safety margin from a rotor with better grooves, but IMO it's not that much more than most people think.
-Ted