Haynes has the service limit at .14inch. Mine are right there. Uh-oh :loco:
You can run them below spec. NOT recommended but doable, as long as the rotor is NOT cracked or showing "warning signs" of fatigue. Tip, if you choose a softer pad the rotors will last a very long time compared to a sintered model.
With a thin disc, danger that the pistons can get hung up is my understanding.
EBC has a GREAT replacement rotor worked up for the K 75.
http://tinyurl.com/motobrickrotorsI installed a pair on Pete's 1992 K 75 S, far superior to the OEM disc.

EBC ProLite XC contour rotors are the toughest and yet the lightest sport and race brake rotors you can put on your bikes for many reasons and here is why these are best.
1) Contoured profile reduces weight by 7.5% without reducing actual “cooling mass” of disc.
2) New German mill rolled heat treated stainless steel rotor blade.
3) Vertical scraper slot system removes dirt, dust and debris quickly from braking area.
4) Unique fully overlapping vent hole pattern reduces weight, cleans disc blade and helps deglaze pads.
5) New Patented Stainless Steel SD (square drive) button drive system, prevent warping and vibration totally system – click here for full tech info.
6) Ultra lightweight ductile alloy centre hub.
7)Use of SD system allows less drive buttons, in the case of EBC we are down to six buttons
8) Full stainless components, no rusty parts and that’s guaranteed.