One very important thing to consider when considering rate of climb is how fast the aircraft is moving forward as it moves upward. For instance, at the right altitude and speed a 1940 Zero could climb (briefly) at 5000 ft/min, about the same rate as a Spitfire XIV of 1944. The differrence is that the Spit would have been climbing at a more shallow angle from the horizontal, but matching the Zero's vertical velocity due to it's greater horizontal speed. Hence, if the Zero were on the tail of the Spitfire and both were at their optimum climbing speed, the Zero might have matched the Spit in vertical velocity but all the time the Spit would have been opening the gap between the two very quickly. Alternatively, if the Spit were on the Zero's tail, it would be climbing vertically at the same rate as the Zero but would overshoot it very quickly.
I've often thought this is a little understood consideration when considering the relative climb rates of fighters. It seems that generally the fighter that climbed with a greater forward speed had the advantage in that the pilot could dictate the terms of the fight. I'd be interested to hear from anyone more knowlegable on the subject.