Check out http://www.notebookcheck.net/NVIDIA-GeForce-GTX-770M.88995.0.html
Then compare against the 780M.
However, as oczdude said, you should really (if you can) consider the higher end gpu then, if needed down the line, replace the OS HDD with an SSD since, critically, replacing a gpu in any laptop is VERY expensive!! and the laptop will very probably not have the space and thermodynamics for future significant gpu replacement.
On the other hand, replacing the HDD/s with an SDD can, in most cases, be done by the user (the drive cover/s normally easily accessible under the laptop).