The TKC80's seem to last pretty well on the front. I've been running them on a previous BMW800GS as well as on the Ten. They give fair mileage, cling to the road and do well off-road.
But at the back there are many choices. I used to run Mitas E07 on the back which lasted well on the 800GS, but gave me only 3400km on the 660.
Due to good feedback from a friend, I've just fitted a Pirelli MT90 and it clings to the road very well. It also does well off-road, but I'll be able to tell after the weekend when we're doing a long off-road trip with gravel, stones, mud and sand.

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2014 XT660Z - Barrett pipe, DNA stage1.5, Barkbuster hand guards and handlebars, Pivot pegs, Teknik suspension, Guard-it engine protector combo, B&B rear rack, Trax topbox.