As you are only running Wordpress (from what I understand), I don't think you require a dedicated server at this point unless you are using a lot of bandwidth. I would go for a VPS, or even a shared hosting account if its feasible.
However, if you really need a dedicated server, maybe you should get something less powerful than an i7 or E5405 as is really overkill for Wordpress sites. A Celeron will do.
I'd go for the two E5405 setup myself, since the Harpertown is a great processor. Keep in mind that the processor isn't the only thing that matters, optimizing Apache, MySQL as well as having a good amount of RAM and disk I/O will help.
It is somewhat confusing to understand what you mean by "6000 thousand", and what sort of media you are referring to.
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