Well the total address space and fact you get twice the memory bandwidth with a good 2xx setup is always a good bonus.
A nice alternative to going whole hog on a dual opteron system is that you could get 2 cheaper single core opterons's giving you similar cpu performance to a dual core opteron for about the same price as 2 single core cpu's (cpu's only) with the bonus of extra memory bandwidth and size and the extra IO and expandabilty that comes with most dual boards
Then at later stage you have great upgrade going to 2 dual cores when they are cheaper.
(thats what I have done, 2x 246's 2G mem on a h8dce)
You really should not Overclock a server or workstation, doubly so if youy rely on it for income, becasue you will be losing money/business while its down.
Having said that my 2(old) 246's overclock quite nicely to 2.4G(at standard voltage), but I don't rely on it for income.
And almost all dual opteron boards are made to be very stable which is a nice thing to have if you have precoesses that takes hours or days, plus you actually get OC'abilty becasue they are designed to be so stable , thats if you work around bios limitations stoping you fromOCing.
Of course if you do buy to cheaper single cores, you will have many months of dual core cpu's calling to you for an upgrade, even if you don't *need* them...argg the torture, they are calling again "buy me, buy me" /wacko.gif" style="vertical-align:middle" emoid=":wacko:" border="0" alt="wacko.gif" />