Amsteel is what you want. I call it PBO, I'm not sure if thats right or they are the same thing.

Amsteel works great for tramps. I have fabric loops on my tramp that tie off to the sides of the boat, and I used Marlow and it chaffed the webbing. Amsteel doesnt chaffe.
3mm is plenty strong.

Amsteel loops make great replacements for eyestraps. Drill a hole, pull a piece of Amsteel through with a knot on one end or pull the middle through of a piece with both ends knoted.