what do you recommend me to buy because i can buy a gtx 590 if i want
Have a read of this review of the GTX 590.
It has comparisons with the HD 6990 and Crossfired HD 6970's.
Crossfired HD 6950's will give a few percent less performance.
I'll try and give you the information to help make a decision but I can't make it for you.
Other people may be quite happy to tell you what to spend £400, £500, £600 on but I think you should make your own informed decision.
If I was spending my money I'd get 2 HD 6950's for around £400 rather than a GTX 590 for £600.
You may prefer a single card solution even though it's still 2 GPU's on a single card.
I believe there is very little overclocking headroom with the GTX 590 because the cooler can't cope with any more heat.
btw i got sli 460 atm will 6950 pwn them