George - we have been using a 5mm UHMWPE rope on our winch for over 10 years by now. Our drum holds about 5,000ft with some free-board left but the same length of line wound up tight after a launch vs. reeled in under light tension after the last launch of the day makes for a completely different fill-grade of the drum. So, using any number of feet of line on any drum needs to be followed by 'wound up loosely' or 'wound up tightly'.
Also, was this Roman winch converted from steel cable to Spectra or similar? Does it have a level-winding mechanism? If so, there is a marked difference between winding up steel - vs. Plastic line.
Feel free to contact me directly if you have winch related questions: moc.oohay at nnamuenilu
Uli
'AS'