Courtney,
In my own spectatorial experience the F3 could get high and fast for one presentation and that was it. I never saw them maintain 30k and above for any length of time. Maybe it was a trick they were keeping up their sleeve...and as always I realise it's easy to win the debrief from one's own perspective.
I played 'drone' for a F3 dress rehearsal once (AIM-120 shot) and I remember that the shot was on the number going up through 30k ish very fast - but they then had to come back down - very fast. They also always used to fight without tanks - which I am sure was representative as they would have thrown them off in combat - but their endurance always seemed very short in that fit.
By happenstance a F3 chased my Fox 3 and asked politely if we could descend to hold when there was a snag with the range. I couldn't afford to drop down due fuel (Sea jet cost only 65 lbs/min above 30k) - they couldn't afford to stay up with me for the same reason. Being gentlemen and good eggs they stuck with me. Post shot they went home on a bingo profile just as Point Mugu declared itself IFR...poor b#ggers.
Anyway. I'm not slinging spears for the sake of it - if you flew a British aircraft in the period we're talking about - it had significant short comings, that's why we loved them - look at the morale on the Jag force! Awesome community, awesome blokes, somewhat sub-optimal platform...same as ours in the FA2 community...same as everyone else really!
Take care, fly safe.