GeForce GTX 880M 8GB is a high-end mobile graphics card and the fastest as of Spring 2014.
It is based on a full variant of the GK104 Core of the 28nm Kepler architecture and thus offers 1536 Shader Processing Units, 128 TMUs and 32 ROPs, on a 256-bit memory interface of fast GDDR5. While the central unit runs at 954MHz and goes up to 993MHz, in Turbo Mode, the memory clock operates at 1250MHz. The rated TDP is clearly above 100W and 122W, on average.
It is thus just a faster clocked GeForce GTX 780M. Theoretically, its performance might be up to 15% better than its predecessors, but since its memory bandwidth remains the same, expect at most a 10% performance boost, depending on the 3D Game.
Therefore, GeForce GTX 880M will only be seen on very large note books and it needs to be paired with at least 8GB of RAM and a Strong Quad Core. The card is suited for 1080p and even the most demanding games should run fluently at high settings.