need some advice for a futue bl project..

[BP-Revo]

Well, techincally yes, but the difference probably won't be noticed.

An ESC with less resistance will allow more power to get through to the motor resulting in more power.

7XL on 6S will be a little hot, but none the less probably be into the 50's.

8XL, 50's too I think.

XXL Lehner, depending on KV and gearing, anywhere from high 40's to mid 50's or more.

A side note on Lehner motors. One big thing about a Lehner motor is the quality, which makes it extremely efficient. This means that it can produce more power given the same power output (less power loss to heat and other factors).

Don't take what I say as the bible though, since compared to most guys here I'm a brushless noobie, though I know enough to get me by. All those speed estimates are just what I read as typical results from other users with those setups.