1080 g1 2050 core -i 27 405 mh, I think this is stable. 400 mh is stable though with -i 26. 1080 doesnt scale well with overclock. windows 8.1. -i 28 has nonce problems
Mining on a low difficulty can sometimes give Nonce already sendt error messages, but they should dissapear when the difficulty rise. But if you get Nonce does not validate on the cpu, then you should use an another setting.