All I can say is drag is there, big time.
I was cruising on 100% power in a P51 with 2 1000lb bombs and 6 rockets on the wings, when I was intercepted by another P51. I dove away with WEP, but teh other P51 was catching up, even though I was probably over 2000lb's heavier. Once I jettisoned the ordinance, the distance between us stayed constant.