Going from a 1080p 120Hz display to a 4K display costs $200.
It may be cheaper to simply upgrade this laptop yourself, although doing so will void the warranty.
The 6820HK also has the benefit of being a K-series processor, meaning it is unlocked for easy overclocking.

The main piece of hardware in this unit, though, is the Nvidia GeForce GTX 1080.
This rated boost clock is the same as the desktop card, although the core clock is slightly lower.
Thanks to GPU Boost 3.0, though, the notebook card does boost above 1733 MHz in many situations.
Again, this is the same as the desktop card.