The newer the architecture, the newer the Instructions per clock, the more reliable each core is.
Xeon CPU's aren't built with gaming in mine, they're server chips and serve to have higher cores > higher IPC. Of course which each new architecture this improves, but Intel's i5/i7 line have superior single/multi-thread performance, so I wouldn't trust a nehalem chip (that's an extremely old architecture) to push today's games well, especially at a mere 2Ghz.