PCI-Express 2.1 or PCI-Express 3.0

[nick1200]

Ok so in the next few days i wanna get a new gfx card but have found 2 which i like which is in my price range.

http://www.overclockers.co.uk/showproduct.php?prodid=GX-168-MS

MSI HD 6850 "Dual Fan Edition" 1024MB

which i noticed has Processing Cores: 960 but only a PCI-Express 2.1 but then the other one i like has less cores but PCI-Express 3.0

http://www.overclockers.co.uk/showproduct.php?prodid=GX-102-GI

Processing Cores: 512
Bus Type: PCI-Express 3.0

Would the cores be better than the extra pci express ? like which would make the more difference ?
I was thinking about buying 2 of one of these and setting them both up in my computer under crossfire/ sli

 

[akxpckwb]

The 6850 is better than the 7750 in everything except power usage. The 7750 uses very little power (not even requiring a PSU connector) but its performance is weak compared to the 6850

 

[TheBigTroll]

personally, i would get the 6870 since it isnt much more than the 6850 and performs pretty dam well against the 560

 

[clutchc]

From my experience with 2 x HD 6850s in Xfire, they have a problem when it comes to micro-stuttering.
http://www.tomshardware.com/reviews/radeon-geforce-stutter-crossfire,2995.html
Common with mid-range cards according to the article. More-so with AMD cards than Nvidia. May be due to the drivers.

I finally sold them and went with 2 X GTX 570s. So far, no micro-stuttering. In fact, no issues at all.