Want your F5 to be lighter? Shoot with lithium AA's. Yeah, they aren't cheap, but they definitely make the camera lighter. Infinity focus has never been an issue for me on the F5's I've owned. It's possible my current one might have that issue, but can't really test at this time, since I'm missing a couple pieces. Namely the battery clip and the back.
When I carry gear around weight isn't a problem but size is more of a problem.