I've been searching for an answer to this question also.
It appears that most places that sell the wire, don't want to commit to amp carrying ability.
Indeed it does depend on the length of the run.
Here is some info from a website willing to commit to amps:
http://www.ask.com/bar?q=silicone+wi...3D1%26cat%3D54
14Ga. = 35 amps
13Ga. = 50 amps
11Ga. = 100 amps