Beckton is an MP product based on an entirely different socket, LGA1567. It will not be marketed towards desktops or ordinary consumers in any way and will be extremely expensive.
Dunnington is a Xeon product designed to replace Tigerton Xeon processors in servers - it too is no desktop product, and a quick Google will reveal the bulk prices of these chips, which should put you off the idea quickly. Not to mention that it's just three Penryn dies and massive amounts of L3 on one die, not really worth the cost for regular joes.
According to pcwatch, Westmere will be a six-core product based on the Nehalem architecture. Might want to wait for that instead.
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