Upgrade advice

I have a question for you guys regarding possible new rig. My current specs are as follow:

Intel Core 2 Quad Q6600 Kentsfield 2.4GHz (Oc'd to 2.9Ghz)
OCZ Platinum 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500)
ASUS P5K PRO LGA 775 Intel P35
2x WD Veliciraptors
EVGA 512-P3-N973-TR GeForce 9800 GT

I'm looking into building a computer that's based around AMD Phenom II X4 955 Black Edition Deneb 3.2Ghz. HDDs and video card would be ported to this new one. I haven't decided on mobo or RAM. The question is... How much difference would I see with this new rig. I seen some CPU benchmarks and someone noted that there's only about 10% performance increase between Q6600 and the Phenom. Can anyone elaborate? Is it even worth it?