Even at low altitude the P-47 out-zooms almost everything. I think the only planes that are better zoomers at low alt are the Tempest and F4U-4, though I'm not sure.
I've tested zoom climbs quite abit, using the following procedure:
Dive to to sea level and in excess of 400mph. Level and allow speed to bleed down to exactly 400mph IAS...do a 3G pull up into the straight vertical. Hold zoom until it becomes impossible to hold the craft in the zoom. Note the highest altitude regained. (Note: In a pure vertical zoom like this, the G meter will be at zero, the craft *will* be unloaded.)
Using this test, the P-47D-40, F4U-1A, P-51D, and the SpitXVI all zoom back up to about 6,200-6,500. The plane that has an edge clearly enough to be seen in these tests is the P-38, from which I can usually get 6,700-7000. And this probably has as much to do with neutral torque as any other factor.
In AHII, the heavier airplanes do not nessecarily outzoom the lighter ones with advantageous power loading co-alt co-e. And in the real world, wouldn't zoom climb also be a matter of mass/drag ratio along with thrust/weight, rather a matter of "weight" per se?