In my experience it depends on your riding style.If you mince around in high gears changing up early and never exceeding,say,10-11000 rpm then the valve clearances may well go 26k.If you thrash the t**s of your bike,hitting the rev limiter now and again then this will really bed those valves in and close up the gaps much sooner.Had a FZR1000 a few years back.Valve service was 24k but at 16k the engine really lost it's edge and the idle was really rough.Checked the valves and on 2 of them the clearance had closed up completely.This meant the affected valves probably weren't closing fully when hot.Re-shimmed and all was well.Left much longer would have meant burnt valves.
Got 13k on my '04 now....will probably check the valves in the next 3-4k.