FWIW, Samson Rope (the makers of Amsteel) now produce a high temp synthetic line called Tec-12 similar to the Amsteel Blue (12 strand construction). Which can withstand a working temp of 450*, and a critcial or failure temp of something like 900*.
Take a look at winchline.com, they offer up winch lines made with Amsteel Blue, Tec-12, or a mix of the two (IE, your main line is Amsteel, with something like 20'-30' of Tec-12 to go around the drum).
When I replace my current Amsteel Blue 5/16" line (just cause it want to go 3/8" and get the orange rope instead), I'm prolly gonna go with what Winchline offers in the mixed line or get my father to set me up with one of thier souce for the cruise ships and do a group buy via ordering a spool.
The main reason I wont go MP is cause they ignored me at a trade show, whereas the Samson guys damn near ganged up to help me when I told them I wanted to inquire about using their rope on my Jeep. Trivial, I know, but customer support means alot to me. And since MP wasn't willing to answer a question, I figure I wans't willing to give them my money.