bywas aware of it previously but hadn't bothered to test results vs the implied default -preset medium. but I have a Planet Earth episode which ends up larger than input, and which seems to have fucked up keyframes by default, so I either need to deal with it being larger on encode, or see if -preset veryslow brings it down.
the unfortunate thing is if I get really good results from -preset veryslow I might have to go back and re-rip and re-encode some other things...