Plane / Planes / Aircraft / Aeroplane / Airplane appreciation

There is a difference between absolute pitch angle and angle of attack. You can fly vertically upwards with 0° AOA, so there is no constraint on the zoom climb potential imposed by the limiting AOA.

I'm perfectly aware of what angle of attack is, and that it's fundamentally impossible to pitch the nose of an aircraft up (at a constant speed) without increasing AOA. You certainly can't perform anything that might be regarded as a zoom climb (rapidly exchanging airspeed for altitude) without a considerable increase in AOA, and if the AOA limits are as low as the SR-71's appear to be during supersonic flight, it's not going to happen.