Fenwick "Fenglass" rods in that 8'6" length are about as durable a downrigger rod as you'll find. Cost a little more than what's mentioned above, but they have the feel similar to a steelhead rod with the light, slow action of a quality fiberglass DR rod. Also the blank is very condenced which makes it a nice light, thin diameter rod,
Know of a couple of charter boats in this state, who troll with downriggers, that use these Fenwicks.
I use moderate action graphite rods myself.
$0.02

J.D.