Any benchmarks comparing 8800 ultra sli & 9800gx2 ?

I'm thining of adding a second 8800 ultra but i'm not sure how this compares to the 9800 gx2 . I can't find any propper comparisons anywhere. I can upgrade my current eVGA Ultra to a 9800 gx2 for £70 or get a second ultra for around
£250. Money is not the issue here i'm just wanting the faster solution i know with the 9800gx2 there is obviously the potential for quad sli but out of sli ultras and the 9800gx2 which is faster?

£70 to go up to a 9800gx2 is a bargain imo, Quad sli it in the future when prices drop to £250 or so