9800 GX2 is like 2x 9800 GTX but with lower clocks (600MHz Core/1500MHz Stream/1000MHz Memory vs 675MHz/1688MHz/1100MHz). And 9800GTX+ is like 9800 GTX but with higher clocks (738MHz/1836MHz/1100MHz). 9800 GTX+ is practically equal to HD 5750. So GX2 is nearly two times faster than HD5750. But also GX2's power consumption is almost two times higher than HD 5750. And HD 5750 supports DX11.
And for reference to nVidia, a GeForce 9800 GX2 is VERY slightly worse than a GTX 280. The GTX 280 is worse than a Radeon HD 4870 X2, which is basically the same in performance as a Radeon HD 5870. One Radeon HD 5770 is basically the same as a Radeon HD 4870. So yes, a GeForce 9800 GX2 is roughly double the performance of a Radeon HD 5750. - PR-0927
The GX2 is definitely faster, but also runs hotter. 5750 isn't bad, but it's a first generation dx11 card that's mid-lower range. So when games and apps really start to use DX11, the 5750 won't keep up.
Ummm, that's completely wrong.....being "double the performance" would put it in the range of the HD5870....which it's not. Would also put it in the same range as the GTX480...which we all know it can't compete with.
By the context of what he was replying to, I think he was saying a 9800 GTX is about the same as a 5750. So a 9800 GX2 is twice as fast as a 5750, not a 5870 (which nobody said anyways)