Bates hunter jumper saddle (long vs. forward flap)?

I am the exact same height as you, with long thighs, and I use a regular flap. However, in your case, I would probably go with the forward flap if your knee is usually past the knee roll, even when your stirrups seem to be the right length. See if you can find a saddle to try that has a long flag and one that has a forward flap. I would go to a tack store with a good selection of saddles and sit on each to see which flap would be best. See which one you like better before you buy!