At low low speeds, it doesn't seem to give much warning, but better than the F4U, I'll tell ya that much.
Believe it or not, I always found the Pony to be much more responsive than the F4U whenever i fly it. Perhaps it is because it retains so much speed and builds it up almost, if not, more than easily than the 1-series Hogs. It feels a lot lighter and rolls similarly.
Of course turn radius, it cannot match a Corsair, but when the two planes are not using flaps, the P-51 feels better. Still though, if a K4 seems tough for the Pony, try fighting the Spitfire XIV. It seems to have ALL the advantages of the K4 in a duel yet with better turning! I don't think I've ever been able to take a Spitfire XIV down .. not with the P-51D. Any suggestions?