Does two pci-e 1Gb better than two pci-e 512mb??

Having a graphics card with 1GB of RAM (vs 512MB) will increase performance at very high resolutions and high levels of eye candy (like AA and AF), However if your playing at 1650 x 1080 or below then 512MB will be fine.

Adding two or more cards in crossfire or sli doesn't give you anymore video memory, the memory from each card isn't added together.

E.g 2 x 1GB HD4870's in Crossfire still only leaves you with 1GB of video memory

Another example: 1GB HD4870 + 512MB HD4870 will give you just 512MB of video memory.

do you mean it's the best to have (2)512mb with 256bit rather than (2)1gb 256bit?

It depends on what resolution you play at.

1GB cards would be better for high resolution and eye candy, but will cost you more than 512MB

What cards are you planning on getting?

Also what resolution do you play at?

here's the model sir: Palit Radeon HD 4850 Sonic 1GB DDR3 256bit vs. Palit Radeon HD 4850 Sonic 512mb GDDR5 256bit..both are cossfire..

but I also have a 2nd choice pls advice me to have a excellent graphic card coz i'm having a headache..

heres the choices sir(i'm applying for 2 pci-e).pls choose the right one for me sir..

Palit Radeon HD 4850 Sonic 1GB DDR3 256bit
Palit Radeon HD 4850 Sonic 512mb GDDR5 256bit or
HIS HD 4850 IceQ4 TurboX 512 MB 256 bit

here's the model sir: Palit Radeon HD 4850 Sonic 1GB DDR3 256bit vs. Palit Radeon HD 4850 Sonic 512mb GDDR5 256bit..both are cossfire..

but I also have a 2nd choice pls advice me to have a excellent graphic card coz i'm having a headache..

here's the choices sir(i'm applying for 2 pci-e).pls choose the right one for me sir..

Palit Radeon HD 4850 Sonic 1GB DDR3 256bit
Palit Radeon HD 4850 Sonic 512mb GDDR5 256bit or
HIS HD 4850 IceQ4 TurboX 512 MB 256 bit

According to this http://www.palit.biz/main/vgapro.php?id=855

The Palit Radeon HD 4850 Sonic is factory overclocked and has an aftermarket cooler

The HIS card is also factory overclocked and is slightly faster than the Palit card, the HIS card also somes with a good cooler and both have just 1 year warranty.

The Palit Radeon HD 4850 512MB is GDDR5 where as the other 2 are GDDR3, So I recommend the Palit 512MB if your resolution is at or below 1650 x 1080, if its higher then go for the 1GB Palit 4850.

thank you very much for your help sir..