Re: What speed???
Here's a trolling method that is absolutely killer on trout: Row trolling.
Cast a lure that has good slow speed action out behind the boat as far as you can or want to. Let it sink to the depth you want to fish. Then row your boat forward. The erratic speed of the lure just knocks trout in the head. A rod holder's nice, but not essential. You can just lay the rod over the transom and watch it.
Of course, this won't work on a guy's big boat, but it sure works great on a 12' aluminum boat.
BTW, the same technique also works on walleye, northern pike, and muskies. I've hooked the odd largemouth that way, too.
Again, it's an old technique that's pretty much forgotten, but it still works...often when nothing else does.