The abrasion guard is a separate nylon sheath that slides up and down the rope as needed. I would go with the 10' as it would give you more potential protection if needed. I'm not sure of any downside to having a longer one.
Mr. Fox might have some other useful input as he's competed with synthetic rope and has a lot of experience with it.
Rick - did you receive your rope yet and who did you get it from?
Scott from Rockstomper told me to pay close attention to anchoring the end of the synthetic rope onto the winch drum. There needs to be a more substantial anchoring setup as compared to the wire rope. Be careful not to have the rope get pinched between the hole in the winch drum and the anchoring hardware. Seems logical but it took me a little while to get the right mix of hardware and to correctly position the rope. Then again...I'm a little slow.
Silly me. I assumed that the winch line anchor points would be the same. My 8274-50 has a hole in the drum that the winch line passes through and is anchored by nuts/washers/bolts to prevent the line from coming through. Yours sounds like it might be easier to attach but am not sure as I have not seen it. Sorry to confuse.