I have the BOB Yak Plus, and like Nathank, don't believe I could ever overload it. I take regular weeklong unsupported cycling tours carrying everything I need except my main meals and could not be happier.
I suspect the 50 pound weight limitation may be because of the plastic wheel that is standard on the COZ. You might wnat to see if you can upgrade to the aluminum wheel that comes on the YAK if you plan on really using the trailer.
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2003 Iceman Challenge - 2:34:55 - 897 / 2,000*
2002 Iceman Challenge - 2:39:23 - 1093 / 2,186
2000 Iceman Challenge - 2:49:18 - 1516 / 2,153
*estimated