cubeless speaks the truth - if you dont get that x2 to 2.8ghz your performance will decrease (except in well coded multithreaded apps taking advantage of that second core).
And I dont know why, but I get lower memtest86 memory bandwidth report with a x2 4400 1mbx2 than a venice 3000+ ... both confirmed in dual channel mode. Two sticks.
ps- I have an opteron 146@2720 and I wont bother considering upgrading the cpu or the video card again till UT2007 comes out

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Fact of the matter is, if you get a cpu over 2.7ghz, then only performance increase in general will come from a cpu you can get clocked even higher, and in general, 2.8ghz is close to the air cooling ceiling.
pps- if my damned crappy MSI SLI motherboard could actually put out a solid 1.55v I could do 2.8Ghz, but it has no vcore settings higher than that to compensate for undervolting. WHAA