It all depends on the time of year and the weather also the fish,
I troll flatfish as slow as I can .5 to 1.0
pop-gear at 1.0 to 1.5
spoons 1.0 to 3.0
plugs 2.5 to 4.0
alot of the time if the wind is blowing you can drift a flatfish or just a worm.
I've had days up at the berry when trolling with pop-gear and a spinner / lure in the wind at a super slow speed with the wind and every time a wave would push the boat we would get hit / fish "cutts"
I also had good luck drift fishing with flatfish.
You just have to find what the fish wants that day
Also I always do S - turns as I trolling and I'm always
speeding up and slowing down.
But a good place to start is around 1.5 and let the lure tell you how fast.
All good advice Roger. Pretty much the same tactics I use....