getting the files as small as possible is NOT the goal here,
the goal is to get the most stable, edit friendly material.
so H264 may NOT be the answer. i suspect it might take longer to create, too.
for FCP Classic, ProRes is the answer
this is, by the way, the FInal Cut Pro CLASSIC forum, and you might be better of posting in the FCPX forum.
if file size is that important, then drop the frame-size down to SD,
or (again FCP classic info) use one of the Off-line RT options.
nick