RED ALERT DANGER
Some iffy advice in some posts.
Okay, firstly knotting a rope weakens it by about 50%. You do not want to tie knots in your winch rope. Learn how to splice the rope to fix a break, almost no loss of strength that way (carry a fid - they are cheap). Carry extra winch rope, (that's cheap too).
Consider that a winch weight rating is with ONE layer of rope on the winch spool. Two or more layers and the pulling power drops as the effective drum size increases - - kinda like shifting to a higher gear.
My 21 P1000 came with a Warn 4,500 winch with 50 feet of 1/4 inch diameter Dyneema. You do not want to use 3/8" rope on this winch for two reasons. You can't get the full 50 feet on there, not enough room, and you will have less length in the first layers of drum windings so your effective pulling power will be decreased. 3/8" is for the big boys with 12K winches - not us.
Carry enough extra synthetic rope so you can use a snatch block like this:
Snatch block this synthetic line shackle and aluminum ring "block" will do just fine and DOUBLE your winch pulling power - - you just need enough rope to go out and back - - or in some cases to allow a more in-line pull.