At least AMD has released its Quad-Core Opteron CPU and we also have a comparison in term of VMark.
It seems that 16 cores AMD Opteron 8360 SE @2.5 Ghz have a better overall score than 16 cores Intel X7350 @3.0 Ghz (both on DELL Platform R900 and R905).
The VMark Results are here.
((enjoy))