what is the parameter of measuring a good graphics card?

Benchmarks which reflect the cards' relative performance in applications and games are the best way to gauge how well a graphics card performs.

Here's a great place to start comparing—AnandTech.com's GPU Bench 2011:

http://www.anandtech.com/bench/GPU11/188

You can look at specifications like the memory type and clock rate, GPU speed, shaders, etc., but the specs alone don't always tell you the whole story.

Have fun! :-)

Bench marks can give you the run down you need for performance...speed isn't everything! here is another test lab for bench marks. http://www.videocardbenchmark.net/

Not every GPU performs the same way with different test. Some may have higher overall bench marks but not so good marks on specific games. So unless you want to play a specific game, generally the better rated (higher bench marks) will give better results. Take for instance the then awaited 6990 was suppose to be close to the GTX 580..at least equal to the GTX570...as you can see it cant beat the 6950! http://www.videocardbenchmark.net/high_end_gpus.ht...