Upgrade Paths

Ok, my current spec is in my sig, but my mate is looking to buy it off me, so i quoted him £300. I'm looking to invest another £150 roughly, and am looking into different mobo/cpu/gfx bundles


1. skt754 mobo nforce3 agp, fast a64 cpu (3700+ £149 at komplett!), agp gfx card

2. skt754 nforce4 mobo pci-e, same cpu, pci-e gfx card

3. skt939 nf4 mobo pci-e, slower cpu, pci-e gfx

4. skt939 nf4 sli-ready mobo, slower cpu, pci-e gfx

bear in mind i've got to buy a new psu to match as well, which is best?