I just wanted to follow up and say that I tried this setup with both Airvideo and StreamToMe and, man, I feel silly for not having thought of it earlier. it is much better than streaming direct from PC to PS3.
The main reason is the ability to scrub through a video to a specific spot and for FF/ RW controls. streaming hi bitrate stuff to the PS3 basically eliminates FF controls for me (over ethernet, not wifi, btw) and scrubbing isnt supported at all.
also, some files that just straight up wouldnt play on the PS3 are converted just fine on the computer so they now play on the TV where they could not before. so its more versatile than the PS3 for playback.
as for Air Video vs. Streamtome, they both can playback the files while in the background or locked, so thats good. air video has more fine grained options for video bitrates and can disable subtitles. but streamtome has a portrait control option and air video is landscape only - a bit of an ergonomic win for streamtome.
but the experience was eye opening. I would now recommend this setup to nearly everyone who wants to stream movies from a computer to a TV screen. PS3 used to be the choice here, but Airplay, Apple TV, and one of these apps is faster, compatible with more files, has better FF/ scrubbing controls and is a better remote than the PS3 controller.