I agree with BandH. F40 makes the flare a little harder to judge, especially at night. Can induce that tendency to float a little (-800), which can be a right barsteward if you have a slight tailwind and therefore removes the benefits of a F40 landing in the first place. I am relatively new to type, so it's a problem I am overcoming. I find my landings using F30 are much better as I find it easier to judge the flare (plus the shorter spool down period), however it doesn't stop me from selecting F40 for performance reasons.