You should listen to me. No, seriously, listen to me.
Join Date: Oct 2008
Location: Santa Barbara
Motorcycle: Blue 2006 GSX-R1000
Re: GSXR 1000 k1 cranks slowly
Anything is possible but two weak starters seems unlikely. Measure the battery voltage when it cranks. You could also measure the voltage at the starter terminal. I'm thinking that one of your connections to the battery, starter, starter solenoid, or engine block (main ground) isn't tight.
You could also remove the valve timing inspection plug and try turning the engine over by hand (service manual 3-16). I don't have a torque value but if it's hard, you could try removing the plugs.