New VMmark benchmark results highlight that the best performance for a single server is a 4-socket (or 16 cores with Quad-Core processors). This means that the R900 and R905 are at the top of the list, with the Intel based R900 slightly ahead of the AMD based R905. So if you absolutely need the most performance possible from a single server - then this is the way to go.
A little bit of analysis could lead you to believe that the 2-socket (or 8 core) servers are actually better performing. The VMmark score for the 4-socket R900 is 14.23 with 10 tiles, but the VMark score for the 2-socket 2950 III is 8.47 with 6 tiles. So on a per socket basis, the two-socket 2950 III is actually providing more performance. The same holds true for the two-socket M600 blade and two-socket R805 2U server.
There is much more to choosing a server than the results of a single benchmark, but I think that these results are fair barometers of performance. In general performance does not scale in a linear fashion when moving from 2-socket servers to 4-socket servers, and this seems to hold true with virtualization.
Todd
