NVIDIA has debuted five new mobile GPUs for the mainstream and performance segments of the market. Ranging from the new GT 720M all the way to the new 750M, these GPUs all support NVIDIA's "GPU Boost 2.0" technology. GPU Boost dynamically changes the clockspeed of the GPU to save power when possible.
The new GT 720M and 735M compose the mainstream segment and the GT 740M, 745M, and 750M are destined for the performance user. While your current system may be a generation behind, it's highly unlikely that your older 680M will be eclipsed by the new 750M.
NVIDIA says that the new line of GPUs will be supported by all major notebook manufacturer in the coming months.