If flatwater speed is what you're after, with the capability of surfing wakes, etc. then the Mako 6 is the better choice. It's hands down faster than the S1-R, which I own. A friend has the carbon 6. I've paddled it; it's a rocket. The S1-R is significantly more stable though, a superb choice if you enjoy going out in big conditions, or if your skills are not quite up to that level (like mine). Had my Huki out Saturday in 4-7' swell and confused wind driven fetch with gale force winds-it was supremely stable. Opting out the S1-R with the 4" rudder will increase speed, but still not to the point of the Mako, and the S1-R does give you the option also of a kick up rudder for shallows. Interesting feel to the Mako; it feels nervous right at the onset, but two or three paddle strokes in, it firms up wonderfully at speed. Picks up and flies like a bird on the slightest swell also-the single footwell and narrow 'fit like a glove' cockpit and catch invite proper rotation.
"Nice? It's the only thing," said the Water Rat, solemnly, as he leaned forward for his stroke. "Believe me, my young friend, there is nothing -- absolutely nothing -- half so much worth doing as simply messing about in boats."
'The Wind in the Willows'~Kenneth Grahame