System upgrade - opinions on this please!

Hi! Looking to upgrade my system and do not want to mess it up . .

this is what I already have, I have under £400 to spend:

Operating System:
Windows 7 Ultimate (x64) Service Pack 1
Case:
Cooler Master Elite 335 Case - Black
Motherboard:
Asus M4A78-E AMD 790GX (Socket AM3) PCI-Express DDR2 Motherboard
Memory:
Corsair XMS3 4GB (2x2GB) DDR3 PC3-10666C9 1333MHz TwinX Dual Channel (TW3X4G1333C9)
Graphics card:
XFX ATI Radeon HD 4850 "XXX Edition" 512MB GDDR3 TV-Out/Dual DVI/HDMI (PCI-Express) - Retail
Processor:
AMD Phenom II X3 Tri Core 720 Black Edition 2.80GHz (Socket AM3) - Retail
Power:
OCZ StealthXStream 500w Silent Power Supply
Cooler:
Sunbeam Core Contact Freezer CPU Cooler (Socket 754/939/940/AM2/AM3/LGA775)
WD 1TB 3.5" SATA-III Caviar Green Internal Hard Drive - 7200RPM 64MB
Philips 221V2SB TFT LCD Full HD 22" DVI Monitor
Pioneer DVRS19LBK 24x DVD±RW DL & RAM with Labelflash SATA Optical Drive

And this has been recommended....

Intel Core i5-3570K 3.40GHz (Ivybridge) Socket LGA1155 Processor (77W) - Retail £179.99
MSI HD 6850 "Dual Fan Edition" 1024MB GDDR5 PCI-Express Graphics Card £83.99
ASRock Z77 Pro4-M Intel Z77 (Socket 1155) DDR3 Micro ATX Motherboard £77.99
Samsung Green (MV-3V4G3D/US) 8GB (2x4GB) DDR3 PC3-12800C11 1600MHz 30nm Dual Channel Kit £41.99

Total (inc P&P and VAT): £395.35

any opinions??? Thanks!