e_degala et al., my ensuing statements are NOT recommendations of what you should do. Do only what you think is safe. I take no responsibility for anything you may do or not do correctly, or for anything that may happen. I am merely reporting what others have done and what I plan to do:
I have knowledge of someone in Michigan with a GTS running a 75 NX shot with the PowerFC at the track with no problems. He runs the highest octane he can get, uses two degrees colder spark plugs, uses one step higher fuel jet than what NX recommends, and has the PowerFC tuned halfway between street use and track use (since he doesn't have the backordered Datalogit to switch back and forth between maps).
The result is 13.6 s at 104 mph at 900 feet elevation, and he claims he is not driving the car to its full potential. I can see a perfectly driven car with nitrous-tuned PFC, and nitrous kit (duh), hit 12.9-13.2 at sea level (depending on the extent of other modifications, weight reduction, fw, super lightweight rims etc).
The advantage of the PFC over the stock ecu, is that the ignition timing can be retarded to reduce knock to acceptable levels (depends on the individual). Also the A/F ratio can be adjusted to run richer to play on the side of safety.
Detonation is the primary cause of engine damage from nitrous. The PFC with Commander or Datalogit can monitor detonation/knock level. If you make the correct preparations, it is my opinion that 75 shot is safe even with the NX kit, which is rated at the wheels. Other kits are theoretically safer since they are rated at the crank.
I know of someone in SoCal with a GTS who ran a NX 75 shot w/o PFC and took the necessary precautions to run with no problems. He ran a 13.716 s at 99.89 mph at 1200 ft at California Speedway. He did not retard his ignition timing. With PFC and at sea level that time would have been much better. I wrote that he "ran nitrous" because he runs a stafford turbo now. I have a video of the above person running with nitrous, and that video is a part of Lucky_317's video collection.
Both of the above persons used a Mallory window switch.
I plan on tuning my PFC for use with Zex kit once I get the Datalogit. I will be using 100 octane fuel, two heat ranges colder spark plugs, and retarded ignition timing. I have a Mallory window switch and the two individuals mentioned above have instructed me on how to wire it with my nitrous kit (the one with the PFC is a pro auto electrician). I will dyno-tune cautiously at first and build until right before I reach the knock level I am willing to tolerate. I believe that a 100 shot would likely blow a stock motor at some point. I wouldn't do anything I think may blow my engine, so I will run a Zex 75 with tuned PFC and ALL of the mandatory precautions. Even with 11.5:1 compression on the GTS, I believe 75 is safe if done right.
I believe 99% of the people who have blown their engines with nitrous, across all makes and models have done so b/c: 1)they didn't follow directions which may include 2) not using higher than premium gas 3) not using 2 heat ranges colder spark plugs 4) not retarding ignition timing 4) running lean b/c of problems they had prior the nitrous install (Intake
causing lean code, problems with fuel system, etc) 5) hitting the rev limiter with nitrous on 6) running the nitrous too long 7) running with too hot a bottle 8) trying to run too big of a shot for their motor 9)and of course...trying to run nitrous period on a cheap car with a cheap engine, and other ignorant acts...
The 1% may include individuals who should have had a sturdy engine but got a defective engine from the factory, or other dumb things like poor maintenance, e.g. low motor oil which would blow a N/A engine. And other random stuff they blame on the nitrous: like running an aftermarket crank pulley (but let's not get into that, that's another discussion).
I thought I would share what EXPERIENCED people have encountered, as opposed to hearsay (which may include individuals who did foolish acts).