The description of PFs in SFB says they're about 35M long.
The scale of PFs in SFC's model.siz file makes a PF from about 17% the size of a CA for the Roms and Gorns to about 30% the size of a CA for the Lyrans. I'm not sure why the Lyran bobcat is so much bigger in SFC. All PFs should be about the same size.