Alienware 17 R3 Graphics Amplifier Question

I have the latest Alienware 17 R3 with an i7-6820, 16GB RAM and GTX 980M 8GB GTX. Had this laptop about a month now

My question is is the amplifier compatible with my laptop being the 17 R3 as the website just says 17 R2 and will it be worth it me buying one and putting a desktop 980m 4GB into it. Will I see a massive difference in performance and framerate to run games on ultra settings ?

To spend a further £150 on an amplifier and then another £300 odd or so on a GTX I need to know is it worth it