The Sager NP8672 I'm seeing is:
http/www.xoticpc.com/sager-np8672-clevo-p670sg-p-7800.html?wconfigure=yes
Notes on this model:
Comes with 8GB of RAM standard.
Comes with INTIGRATED 980m with 4GB VRAM
Non-upgradeable processor meaning it is soldered on board
Base MSRP: $1521.93
Notes on NP9377:
Comes with 8GB of RAM standard
Comes with DEDICATED/USER UPGRADEABLE 980m with 8GB VRAM
Upgradeable processor so you can always replace it if it goes bad, or you have it for a few years and are able to buy a faster one cheaper.
Base MSRP: $1764.43
Go with the NP9377, hands down, no questions asked if $1800 is your limit. That one also has a user customizable colored keyboard. My friend has an MSI with this and it is a wicked cool gimmick. Since the NP9377 has the option for SLI, that means you have TWO slots for a dedicated GPU. You will be able to purchase another 980m down the road and add it to your notebook for SLI performance and a total of 16GB of VRAM. Holy crap, that means your laptop SHOULD be able to go beyond the 4K standard as this mainly pertains to not only the GPU power itself, but the amount of VRAM you have. The 980Ti only has 6GB of VRAM and that is pleeenty for 4K gaming. (No idea at all why the 980M has twice the VRAM of the desktop equivalent.
All that out of the way.. The custom copper cooling and better thermal compound will bring the price to $1875.01. I recommend at least the copper heat sinks since they are custom for that model and will keep the beast cooler. The thermal paste is $35 but will also help, plus I am not sure if adding your own will void the warranty. Doing it yourself will cost anywhere from $5 using Arctic Silver 5 to $15 if you go with CoolLaboratories Liquid Pro/Ultra. Probably best to let them go ahead and do it.
Next, mSATA SSD. 120GB/128GB depending on brand will add an extra $100, you could sacrifice the thermal compound to save $35 if you'd like. Just go with the copper, trust me. An extra $60 will get you a 250/256GB SSD. I recommend the smallest SSD at least to have the OS drive and some applications to have opening programs and general OS performance at very fast speeds.
It comes with a 1TB SATA II (3Gb/s) 7200RPM, which should be fine for all your media and games. Only reason to get an SSD for games would be to decrease loading time, you may gain 1 or 2 FPS as it will not affect game play.
With the SSD you are looking at a grand total of $1972.01. If you'd like to cut that back I don't see any problem with just sticking with the 1TB HDD and negating the thermal compound. You will have an extra HDD bay free so you can always go on NewEgg and find a deal on a 250GB+ SSD for waaaay cheaper than they are offering.
Hope all that helps!