Lately, i've been reading reviews and forums discussions about the G53SX from asus. I found out that it only got a 128bit GTX 560m installed while the others have 192bit. I've also read that it is just nowhere good as a 192bit GTX460m.
If it has 2GB of VRAM it's a 128bit model.
The performance is a bit less - but it's still well above the next step down to the GT 555M and really not that far away from the GTX 460M. NVIDIA GeForce GTX 560M review
"GTX 560M (192bit) was on average 13% faster than the old GTX 460M"