My model m14x r1(upgraded to 8 gigs ram).. I bought last year(2015).. Not knowing much about alienware at the time, and impressed by the lighting system, and thinking it was a up-to DATE gaming machine, paid 500$ for it, thinking it a good deal... Heres the thing, generally its good for ALL older games, and even had allowed me to play a LOT of newer games, NOT at great framerates, but generally playable... Examples are mortal Kombat X(average 30 frames a sec, low settings), fallout 4(maybe 25-35 FPS, lowest settings generally), Shadow of mordor(maybe 40 fps on low settings) and even Mad Max(35 frames a sec)...
Now, some of these games, looking at my specs, I shouldnt be able to PLAY THEM AT ALL!! My card is the Geforce GT 555m.. May of these games are so far out and shouldnt be playable at all.. Especially considering how LOW my processor is considering what the requirements are(My processor Intel I7 2670qm, 2.20 Ghz(quad core hyperthead)... So how can this be explained? My MAIN concern is I really want to play the NEW DOOM, requirements for that are ALSO way above my system... And is there anything I can do to SERIOUSLY improve my framerates for NEWER games on this model(and no, I cant buy another computer, Im very poor).. Just looking for advice on HOW my alienware has been able to play these games that are far beyond my specs, and what I can do to further this...
From memory the 555's are only 3GB GDDR3's so that pretty low to start with.
Your very limited in your options for improved framerates and anything you do will only improve things slightly, weather it will be enough to play the new doom I can't answer.
So, considering your GPU is soldered to the motherboard and therefor completely unupgradeable you'll have to focus on other things.
A faster CPU will help slightly, it can be set in NVidia control panel to take the PhysX load instead of the GPU, maybe a 2860QM or if you can afford it a 2920XM
Next max out your RAM, your rig will take 16GB, you wont notice a lot of improvement by itself but your chasing every little bit you can right now so it all adds up.
And your HDD, Solid state drives are cheap as chips now and you will notice a improvement with this upgrade.
And finally - Learn how to overclock, I would not go overboard with your rig but a minor overclock coupled with the above upgrades may just put you over the line for Doom.