video card speed

Hey what is the main factor in determing video card speed/preformance im looking at some card specs right now and i see a few things:

or actualy how about i show you the three im looking at right now and you can tell me which is the best:

http://www.newegg.com/Product/Produc...82E16814130226
http://www.newegg.com/Product/Produc...TT=Video+Cards
http://www.newegg.com/Product/Produc...TT=Video+Cards

now when i look at this i see that the CHAINTECH SA62A-256 has the highet Core clock speed: 380MHz leading me to belive that its the fastest however its also the cheapest.

The other thing is PixelPipelines. The more expensive one says it has more so perhapse this is the main factor in determing speed.