Those processors are fairly old, most modern quad cores will get you similar performance.
A modern Dual 6 core will heavily outperform that.
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As you can see, the dual X5650 stands its own among the modern CPU's quite well in the synthetic benchmark (not too useful in real life, but actually more relevant to things like video encoding). It's faster than the single E3's and not much slower than the modern 6 core E5's.
Now consider the fact that the dual E5's will likely cost several times that of the dual X5650, these're actually of some *excellent* value.