I'm just learning to troll plugs, but no flasher with a plug (probably mess up the action. In fact, a guide friend recommended against a flasher for Nehalem Bay with herring, but I think he was talking the Wheeler area, since at the jaws everyone was using them). I've used both a jet diver on about an 8" dropper, which is clipped on as a slider above the bead chain above the leader (about 5'). I've also used about 0.5-1oz of lead on a bit longer dropper.
The Maglip 4.5 dives deep enough, I've been told they can be flatlined (no weight or diver). With 70-80 feet of line out, they'll supposedly go down over 20', depending on current/troll speed/etc. Which seems deep enough for the places I fish (except near the jaws, where it's slightly deeper). I think K15's get down pretty good, too.