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We're using 1/4" vectran rope from McMaster, which has a working load of 1500lbs. Make sure whatever rope or cable you're using has a WORKING LOAD in the range you want that that you're never exceeding any bending allowance.
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The problem with UHMWPE is that it's used for so many different purposes and it's properties change so easily that they never rate it for working load, only breaking strength. The actually working properties are pretty interesting, the molecular bonds are fairly weak (Van der Waals forces hold it all together), but the molecules are very long, so the surface area between the molecules is enough to provide a lot of strength. That force changes pretty quickly when there's any kind of bend in the line, temperature difference, if it's wet, if it's a Saturday.... Vectran is quite a bit more stable, but lower strength per cross-sectional area, which is the reason we went with UHMWPE (not to mention price, it's a little older and proven material, and used more commonly in commercial applications like boating and rock climbing).
Thanks for all of the suggestions, this is very helpful!