If you are in FW trying to escape you would dive, not go into sustained climb at 250 mph. Most spit pilots would just lose ground and climb at a higher rate then dive at the FW.
Plus any speed advantage held by the FW in level flight will diminish as you start climbing. Any attempt to climb away from a spit is stupid. The point is that around 250 mph sustained climb the planes should be evenly mathched.
That is not to say a FW with superior energy would not zoom climb away to take the intiative in a fight.