CGMiner Settings for HD7970 GIGABYTE GV-R797OC-3GD - F80 BIOS

I've just bought 2 x GIGABYTE GV-R797OC-3GD cards and they have come with F80 bios.
Has anyone got a decent hash rate out of these cards?

CAT 13.4
CGMiner 3.3.1

GPU-Z reports the bios of the new cards as 015.034.000.002

My existing GIGABYTE GV-R797OC-3GD cards have an F71 bios - GPU-Z reports bios as 015.025.000.007
My existing cards run at 720kh/s at 1043 GPU and 1500 Mem.

Any clues as to the best settings for the new GIGABYTE GV-R797OC-3GD - F80 BIOS cards?
I cant get more than 550/600 kh/s out of them and the same 1043 and 1500 clearly does not work.
All my cards are Rev 2.1

Can I flash the F71 bios onto an F80 card? Gigabyte suggest only the same series can be flashed i.e. F70 to F79 can be flashed. F80 would have to be flashed with a bios between F80 and F89.
Have they changed memory supplier or something?

Thanks for any advice...