I use kojaks and love them. I did some testing a couple of years back with a power meter round a velodrome on my swift with a number of tyres, and with a range of pressures too. The test was to ride at a constant speed and note how much power was required to maintain that speed. Kojaks were the fastest, and were faster still at lower pressures than the max rated (I presume because they give some suspension, which helps small wheels). Marathon racers were the next fastest. For me the best think about Kojaks is that they are fat enough that the pressure you need is low enough to run them tubeless. I run them tubeless with a stans rimstrip, with stans fluid inside so if I puncture it seals itself as I ride, just needing to add more air

Kojaks don't last that long, but at only £15 per tyre here in the UK that's fine by me. They give great grip in wet or dry and their size and suppleness definitely gives some suspension effect which makes them faster.

I'm not running Kojaks now, as over the winter I've been running the swift with 24"/520 airnimal wheels (which you can't get Kojaks for). I'll be putting 406 wheels and Kojaks back on in the next week or so in time for the Smithfield Nocturne folding bike race (in which 20" wheels are the max permitted size).