Yes you can mix and match your processor and graphics card to get better performance. The bigger problem you got to overcome is finding a laptop where you get the option to choose which processor and graphics card is installed as these high end laptops are very hard to find. In the vast majority of laptops you cannot upgrade the graphics card as it is either soldered on-board or, more commonly these days, part of the processor. I would suggest looking at the likes of Clevo chassis's, msi and Alienware. Most Clevo chassis's are usually rebranded by the reseller distributing them.