16.8 vs 18
When I was doing my research most folks that had a good amount of time in both boats reported that the Taran16 was pretty much as fast as the Taran18 except in dead flat conditions. I think in a race situation that you may notice a bigger difference, wth the 18 being faster, but with normal to heavy paddling in average to rough conditions they’d be about the same. Nobody reported the Taran18 feeling slower though.
According to the builder the only difference in hull is the the length (18’ vs 16.8’) and the width (20.5" vs 20.25"). I image it would be similar with the QCC.
I’m not so sure about the planing thing. I do know the my paddle strokes feel a lot easier when the boat gets up to speed. On the Taran that happens very quickly.
karma
I have a rather fast boat, but I am a slow paddler. This delicate mix keeps my karma balanced.
speed
It depends greatly on conditions as well. I have a sit on top older model Perception Swing, my friend has a newer peddled rudder boats _ I forget the brand. During a weekend kayak camping trip on Lake Tahoe, the winds came up, we were in white cap conditions, she had to hug the coast because her boat did not handle well. Mine did fine…