7970 Litecoin Mining Help

[notaek]

So I have a 7970. On one BIOS, the highest voltage is 1170 mV.  I usually mine litecoin on this BIOS at a speed of 600kH/s when my GPU Clock is at 900MHz and my memory is at 1575MHz.  When I switch over to my other BIOS, which allows me to crank the voltage up higher my litecoin speed goes way down.  At 1015 core and 1760 mem (I'm sure I could even go a little higher than this) I only get 400kH/s. 

Does anybody know why this might be?

[Vezunchik]

Hardware errors, I think. You may set lower intensity to avoid this.