I can filter for packet lengths using a display filter containing data.len >= XXX, but I'd really like to use a capture filter for this for efficiency... is there a way to do it?
As you said in your comment:
greater <length> less <length>
They also happen to be in this handy tcpdump cheat sheet I have on my wall.
Wireshark uses the same capture filter syntax as tcpdump, and it doesn't look like that's an option