The GeForce GTX 965M will probably be equipped with up to 4GB of GDDR5 memory with a frequency of 5000MHz and has a core clockspeed of 944MHz (plus Boost).
According to Notebookcheck GeForce GTX 965M will replace GTX 870M, despite worse specs (at least on paper). However, thanks to larger caches and new color compressing algorithms both cards perform equally.
Source: VideoCardz