Xeon vs Opteron architecture, which has the fastest memory bandwith ?

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I am currently trying to figure out what would be the best
configuration for a cluster that will be bought very soon. Having only
a limited understanding on architectural issues (and seeing various
contradicting opinions and benchmarks), I would like some information
to help clarify this, and eventually know what you recommend for a
cluster. The biggest constraint is that it has to run linux on a x86
architecture (due to the codes we are planning to deploy on it, namely
starCCM+ and OpenFOAM), which tie down the choice to Xeon and Opteron.
Here are some assertions on my current understanding of underlying
problems, which are likely to be wrong, tell me if so.

CPU have become much more performant than memory access, which is
putting a lot of pressure on the FSB paradigm, created times ago, when
memory access were comparatively faster. The CPU cache has been
developped to limit the access to the memory, but, due to the large
amount of data needed to solve Navier-Stokes equations on a large
domain, cache performance become less important as it needs to be
frequently filled with data from the RAM. Hypertransport from AMD is a
solution, has it removes the FSB and allow the Opteron CPU to be
connected directly to memory. However, recent Xeon provide several FSB
(one per core) which also cirvumvent the problem of saturation of a
single FSB, and might explain why Xeon equip a large percentage of
clusters, despite its use of "old" FSB technology.

Is Opteron Hypertransport still ahead of Xeon multiple FSB in terms of
memory bandwith ?

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