Hi, I bought the Titan Nero when it was on offer with the 1GB hd4850.. I only had like £400 then but been paid now, so what should I upgrade? 
Case Coolermaster Elite 335 Case - Black
Graphics Card Powercolor ATI Radeon HD 4850 1024MB GDDR3
Hard Drive Seagate Barracuda 7200.12 500GB SATA-II 16MB Cache
Memory Kingston HyperX 4GB (2x2GB) DDR2 6400C4 800MHz Dual Channel
Motherboard Gigabyte GA-M61PME-S2P nForce 430 PCI-Express DDR2
Optical Drive LG GH22NS30 22x DVD±RW SATA Dual Layer ReWriter
Power Supply OCZ StealthXStream 500w Silent ATX2 Power Supply
Processor AMD Athlon 64 X2 Dual Core 7850+ Black Edition 2.80GHz
Currently have this overclocked @ 3ghz
Processor Cooler AMD Black Edition Approved CPU Cooler
Sound Card High Definition 7.1 OnBoard Sound Card

Case Coolermaster Elite 335 Case - Black
Graphics Card Powercolor ATI Radeon HD 4850 1024MB GDDR3
Hard Drive Seagate Barracuda 7200.12 500GB SATA-II 16MB Cache
Memory Kingston HyperX 4GB (2x2GB) DDR2 6400C4 800MHz Dual Channel
Motherboard Gigabyte GA-M61PME-S2P nForce 430 PCI-Express DDR2
Optical Drive LG GH22NS30 22x DVD±RW SATA Dual Layer ReWriter
Power Supply OCZ StealthXStream 500w Silent ATX2 Power Supply
Processor AMD Athlon 64 X2 Dual Core 7850+ Black Edition 2.80GHz
Currently have this overclocked @ 3ghz
Processor Cooler AMD Black Edition Approved CPU Cooler
Sound Card High Definition 7.1 OnBoard Sound Card