help w/ my pc upgrade..bottleneck issues

[jprovido]

hi to the very helpful guys here in techimo. im back again w/ another question

im considering to upgrade my current computer. my current specs is the following
Athlon 64 x2 7750@ 3.2ghz
asus m2n68-am (am2+Hypertransport 1.0 and PCI-E 16x)
2x2gb team xtreem rams
WD 500gb 16mb cache
Palit HD4870 1gb ddr5 dual ed.@turbo mode

my 3dmark score is 12100. as you can see its low if you consider my graphics card being a HD4870 and its at turbo mode(factory OC switch for palit) and my procie is overclocked at 3.2ghz (from 2.7) im wondering if what is the cause of my bottleneck. im planning to upgrade my procie (pref. phenom II 3x 720) or a gigabyte am2+ mobo hypertrasport 3 pcie-2.0 GIGABYTE - Product - Motherboard - Overview - GA-MA780G-UD3H (rev .1.0) apparently my curent mobo (asus m2n68-am) supports the phenom II procie that im planning to upgrade, im guessing it wont work on its full potential on my mobo, hopefully not

im wonderin what should i upgrade first. my mobo or my procie? and which upgrade would increase the performance of my pc(3dmark score) thanks a bunch guys