Hello, you know I have the same issue and I have an inferior computer compared to yours, and I still can not figure out how to fix it, I have tried many things, even contacted Steam Support and they still can not help me. There is many things people say, things like the game having a memory leak issue, but then how does everybody play? My issue is no matter what, what low resolution, i get a lot of screen tearing, lot of fps drops that get me killed, I have tried many things and none have worked, there is a lot of people with issues, people with good Intel rigs and with good AMD rigs, it is the game because I can run Bf4 fine, i am sure you can run other games fine too,so it is the game.
At this point nobody knows for sure, you can try this : Go to
C:\Program Files\Steam\SteamApps\common\Counter-Strike Global Offensive\csgo\resource\flash
(the flash folder from where you have your cs;go installed) and from that folder, select and delete BACKGROUND file.
Background file is a Shockwave Flash Object, just like the one that makes browsers crash.
By deleting that file you will fix your fps drop problem + you'll also get few more fps (2-5).
I tried this it did not work for me,it works for some people, this is from a CS GO guide on STEAM, try it, if it does not work, I do not know what else to try as I am on the same boat and I have inferior specs compared to yours.