you mean
N2O right?
I would say that spraying 300hp isn't any 'safer' with 8.5:1 compression than it is with, say, 16:1 if the tune and fuel octane aren't right... you can obviously make more power, and get a more efficient burn with higher compression, thus it is more desirable to run more compression with nitrous. Eric4Nitrous, as well as Bill Glidden, who did Eric's motor, both run around 16:1 and spray a WHOLE lot more than 300hp.
It's all in the tune when we're talking 'safe', because, face it, with nitrous you are eventually going to hurt a piston or have some sort of backfire, that's what finding the right tune is all about. Learn from your mistakes, take good notes, and progress from there.
Nitrous likes compression...