try without tc & itensity 17 -19?
my config for 280x (on windows 14.6 driver):
--algorithm bitblock -o server -u user -p pw -I 19 -w 64 -g 2 --gpu-engine=1150 --gpu-memclock=1250 --no-submit-stale --gpu-powertune 20
~2.85 mh/s no hw errors
Thanks for the tip, trying it now.
Worked a treat, thanks again.