Which has the better performance as cost is pretty much the same. As far as i can see the 550ti beats it in most aspects except the memory interface. I am in a right pickle haha 
£168
Graphics Engine GeForce® GTX560 Ti
Bus Standard PCI Express® 2.0
Video Memory 1G GDDR5
Engine Clock 830 MHz
CUDA Cores 384
Shader Clock 1660 MHz
Memory Clock 4000MHz (1000MHz GDDR5)
Memory Interface 256 bit
DVI Max. Resolution 2560 * 1600
DSub Max. Resolution 2048 * 1536
D-sub Output 1 x DVI-to-D-sub adaptor
DVI Output 2 x DVI-I
HDMI Output 1x Native HDMI (Mini HDMI)
HDCP compliant YES
Dimension The card size is 9" x 4.4" x 1.58mm
£85
Graphics Engine GeForce® GTX550 Ti
Bus Standard PCI Express® 2.0
Video Memory 1G GDDR5
Engine Clock 900 MHz
CUDA Cores 192
Shader Clock 1820 MHz
Memory Clock 4104MHz (1026MHz GDDR5)
Memory Interface 192 bit
DVI Max. Resolution 2560 * 1600
DSub Max. Resolution 2048 * 1536
D-sub Output 1 x Native
DVI Output 1 x DVI-I Native
HDMI Output 1x Native HDMI
HDCP compliant YES
Dimension The card size is 8.46" x 4.49" x 1.61"

£168
Graphics Engine GeForce® GTX560 Ti
Bus Standard PCI Express® 2.0
Video Memory 1G GDDR5
Engine Clock 830 MHz
CUDA Cores 384
Shader Clock 1660 MHz
Memory Clock 4000MHz (1000MHz GDDR5)
Memory Interface 256 bit
DVI Max. Resolution 2560 * 1600
DSub Max. Resolution 2048 * 1536
D-sub Output 1 x DVI-to-D-sub adaptor
DVI Output 2 x DVI-I
HDMI Output 1x Native HDMI (Mini HDMI)
HDCP compliant YES
Dimension The card size is 9" x 4.4" x 1.58mm
£85
Graphics Engine GeForce® GTX550 Ti
Bus Standard PCI Express® 2.0
Video Memory 1G GDDR5
Engine Clock 900 MHz
CUDA Cores 192
Shader Clock 1820 MHz
Memory Clock 4104MHz (1026MHz GDDR5)
Memory Interface 192 bit
DVI Max. Resolution 2560 * 1600
DSub Max. Resolution 2048 * 1536
D-sub Output 1 x Native
DVI Output 1 x DVI-I Native
HDMI Output 1x Native HDMI
HDCP compliant YES
Dimension The card size is 8.46" x 4.49" x 1.61"