All these results being posted without tesselation doesn't count for anything when comparing, because running in dx10/ with tesselation off yields scores significantly higher.
Also here is how i bench it normally:
But when I up AA from 0x to 2x and then up Tess from NORMAL to EXTREME here is what I get:
Which is about 68% of the speed of your GTX 480
Now considering that mine is heavily overclocked 919MHz/1838MHz/3980MHz it sounds about right. GTX 460 SLI is a little faster than GTX 580 on average**. And hte performance gain of GTX 460 SLI is supposed to be nearly 90% or thereabouts on average**. So stock GTX 460 should be close to half the speed of GTX 580.
So I have to agree with OMFGWTFBBQ... If your GTX 580 is stock or only slightly overclocked then the results seem to agree.
** Not sure about the exact scaling on Heaven, but IIRC those are the average figures from some benchmarks I've seen.