It's worth noting that some time in the very near future, current Intel processor prices (at least on desktop processors - not totally sure about server cpus) will be dropping considerably. It looks like that time will be sometime in June, or July at the latest. So, if you do decide to upgrade, I'd say wait a couple weeks or a month if you can, and you'll be able to save a little extra (in relation to server total costs - a lot in relation to the processor cost itself).
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"If to err is human, then I must be some kind of human!" -Me