This is a bit old, but any rope can be made stronger (albeit shorter) by a good, old-fashioned reverse wrap. Very old fashioned -- as in paleolithic Grab the middle with both hands, and twist your hands in opposite directions until it kinks. The kink will be your new rope. Keep twisting. When you run out, knot it off, and you're done.

Of course, if you're in a burning building or whatnot, you don't really have time for that.

I did the calculations on the safety of abseiling with 550 cord over here, in case you're curious:

http://www.daughtersoftiresias.org/bearwiki/Using_parachute_cord_to_abseil_down_a_cliff

A 100 kilogram person slipping 2 1/2 feet and stopping in a quarter second should reliably break 550 cord. And that assumes that you haven't abraded it first, since it's not really that abrasion resistant.