I have two bikes set up with tubeless - one has Ultegra 6800 wheels and 25mm IRC Tubeless Roadlites, the other has Hed Ardennes + wheels and 24mm S-Works tubeless. Tire width comes to ~27mm on both bikes. I like them both, but don't see a performance difference between them and good tubed clinchers. With tubes, I usually got about two flats/year, haven't flatted on either set of tubeless yet.
I can't imagine getting 800 miles from a rear tire. That's about a month's riding for me.
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Regards,
Chuck
Demain, on roule!