Sorry for the delay, I just saw this message.
If the keel strip modifies the speed, I don't notice it. It mainly makes me feel more comfortable with landings since there are lots of rocks in the areas where I paddle.
I prefer the IR backband over the seat that came with the kayak. My strongest preference, though, has been putting a foam block in the center of the kayak behind the seat and using that instead of a backband. It makes rotating for the forward stroke easier and provides plenty of support.