What is the best clock ratio for ATI 5970

whats "best" depends on ur goal w/ the card.
Assuming ur mining btc -
If your after highest hashrate possible(higher power costs, longetivity of card extremely short, high temperatures, less power effecient) then leave the voltage stock and run highest GPU clock possible. RAM speed is fine around 300mhz

If your wanting to conserve the life of the card, run it more power effecient, lower temps etc...
Then leaving voltage between .95 - 1.025 w/ clocks around 690ish / 800ish respectively .. while RAM @ 300 - is pretty nice.

I run my 5970's a max of 1v @ 760-770mhz core when its getting warm out, so the fans dont have to work their ass off to keep GPU @ 70c
The cards run amazing @ .95v 690-705mhz ... nice and cool, they will last forever.
My GPU temp I target to 65c & lower and it seems like a nice medium between temp & fan speed, I adjust clocks / voltages depending on the weather, to try n stay close to that as possible. VRM temps are 70C and below.

One big thing w/ 5970 is one bank of VRM's runs about 10-20 hotter than the other for one of the GPU's... if your VRMs sit around 90C+ 24/7 .. expect them to not last very long. VRMs max temp is around 120C, but they were never designed to do even close to that 24/7

So, double check VRM temp & misc GPU temps w/ gpu-z while mining.

Ive had almost every 5970 Ive owned end up developing bad RAM buffers(wether from blown VRMs or cold solder or w/e) - no longer are able to do 3d, but can BTC mine just fine. So, theres huge inherent flaws to these cards. Many miners sell them under such condition w/o even realizing it.
One of the used 5970's I picked up on here had the same problem, right from the start - luckily I got a healthy refund =)