Advice on upgrading graphics card

[jactac]

hi can anyone offer advice on a graphics card upgrade for my desktop? .. on the windows experience index everything else scores from 6 -7 but my graphics get a measly 3.7 .. can't run Aero without problems so would really like something better ..
posting specs to help .. though I now have 12GB ram rather than the 4GB shown.


Case
STYLISH PIANO BLACK ENIGMA CASE + 2 FRONT USB
Processor (CPU)
Intel® Core™i3-560 Dual Core (3.33GHz, 4MB Cache) + HD Graphics
Motherboard
ASUS® P7H55-M SI: MICRO ATX VALUE MAINBOARD,USB 2.0 & SATA 3.0Gb/s
Memory (RAM)
4GB SAMSUNG DDR3 DUAL-DDR3 1333MHz (2 X 2GB)
Graphics Card
1GB ATI RADEON™ HD5450 - DVI,HDMI,VGA - DirectX® 11
Memory - 1st Hard Disk
1TB SERIAL ATA 3-Gb/s HARD DRIVE WITH 16MB CACHE (7,200rpm)
1st DVD/BLU-RAY Drive
24x DUAL LAYER DVD WRITER ±R/±RW/RAM
Memory Card Reader
INTERNAL 52 IN 1 CARD READER (XD, MS, CF, SD, etc) + 1 x USB 2.0 PORT
Power Supply
450W Quiet 80 PLUS Dual Rail PSU + 120mm Case Fan
Processor Cooling
SUPER QUIET 22dBA TRIPLE COPPER HEATPIPE CPU COOLER
Sound Card
Sound Blaster® Audigy™ SE
Network Facilities
ONBOARD 10/100/1000 GIGABIT LAN PORT - AS STANDARD ON ALL PCs
USB Options
4 PORT USB 2.0 INTERNAL PCI CARD + STANDARD USB PORTS
Operating System
Genuine Windows 7 Home Premium 64 Bit - inc DVD & Licence

 

[keynes]

What is your budget? I'd think that newer cards may bottleneck with a dual core cpu.

 

[Rakk]

What are you using the PC for, cos that will determine what is the best upgrade for you

 

[jactac]

Budget-wise I was aiming for around the £200 mark .. pc is used for some gaming but not too intensive.... but mostly photo editing, streaming videos & tv programmes

 

[keynes]

Hd 6870

 

[jactac]

thank you