how manny card you have ? 6 ? are they 4gb or 8 gb version ?
how much virtuall mem you put ?
put 32 ,48 or 64 gb virtual memory
try -h 895 -dmem 1 ; -h 1700 -dmem 0 ...
It is no matter if 4GB or 8GB. Eg. Gigabyte 480 8GB Samsung.
Cards are 470/480, rig 6 cards. System is Simplemining.pl on USB 16GB.