looking for new nvidia card for laptop

Actually, the GPU in the Asus G51VX-RX05 is technically upgradable. Unlike the vast majority of laptops which has the graphics chip soldered into the motherboard, this Asus laptop uses a MXM 2.1 module (a graphics card format for laptops).

The problem is that it uses a custom "reversed" MXM 2.1 format GT 260m. This means that the MXM module is "flipped / upside down" compared to a conventional MXM module. The result is the GPU chip itself is on the opposite side of a standard MXM module. Sticking in a standard MXM module GPU into that Asus laptop will mean the GPU chip will not be in contact with the heatsink because it will be on the opposite side of the MXM module. In the end this means that you can only upgrade the GT 260m with another more powerful graphics card (MXM 2.1 format) that was pulled from another Asus laptop.

The current standard is MXM 3.0 and Asus does not use a custom design of that format. Which means more recent Asus laptops with MXM 3.0 graphic cards are very easily upgradable... as long as you can find another MXM 3.0 card... ebay.