1/2 + 2 is pretty good.
Basic rules are cannot fly above 10K' cabin without Oxy Mask etc. Using above that will be ~17K' altitude (will vary with type). Cannot fly above 25K' cabin due "bends", even with Oxy.
In JP circles, effect is:
JP3/4 unpressurised Max Alt is FL250 (used to go higher before this rule came in) - I have a JP4 manual showing time to FL350 is ~20mins.
JP5 FL350 cruise possible with Oxy.
Spin entry is min FL150, so in modern civvy terms where Oxy not always used, JP3/4 cannot spin without Oxy, JP5 can.
Hawk - I remember getitng one (just!) to FL480.
Even if not using Oxy, a mask is a pretty good idea with ejection seats to protect face / keep helmet on
NoD