Going SLI with the 8800GT would do the job as well, but yes the GTX 260 is better.
I did notice a big preformance impact upgrading from the X2 4200+ to the X2 6000+
So I guess your upgrade is alright.
GTA iV is playable on my rig.. not @ highest but high / medium
cheers for the replys. i guess ill start with the vid card upgrade as with the cpu it doesn't look like the m55sli-s4 is going to support phenoms anytime soon if not at all as i cant run a Amd X2 7750BE which is basicly a phenom... so might have to ditch the mobo...