For the record, i have seen Amsteel at some boat dealers. Found it when searching the web for my winch line. Problem is, none of the boat dealers had it set up for winching. No eye splice and thimble to attach a clevis hook to. Moreover, they all seemed to charge about twice as much.
Here is a site that has it - not sure it is the best site, just the first one i found.
http://www.okoffroad.com/stuff-winchrope-atv.htm
Amsteel 3/16" is rated at 5,400#, while 3/16" wire is rated at 4,200#
The amsteel is $10 more then wire for 50' of 3/16" - $39.95 compared to $29.95
Factor in shipping and it is only $2.50 more since it weighs 1/6th that of wire.
$47.45 for Amsteel shipped... (and you might even find it cheaper) That's a no brainer. You will save that much in band-aids (or hopefully not, stiches) avoiding the damn wire spurs that tend to slice through fingers...
Hands down, the various synthetic winch ropes are the way to go. Once you use them, you will curse yourself for putting up with wire for as long as you have.