Hmm, Phenom 9500 is actually 8% slower than an Athlon64 X2 6400+. I would still go for the quad though, for daily use. =) I even compared HyperThreading on/off (8 and 4 "cores") and 8 cores was smoother, even under 50% CPU used. The more the merrier in a modern OS.
http://www.newegg.com/Product/Product.a … 6813186166
It’s an old platform though, so you’ll probably have better luck finding something cheaper on eBay. You’ll knock a bit off the price by removing the Radeon HD 3000 onboard from the picture too. The HD 2400 XT your system came with is considerably faster than the HD 3000.