I have HD 6670 which is pretty similar to your card and I used to have fps performance issues in my games with any graphic settings because I didn't use to stabilize my fps. Now I can pretty much use any video settings I want in CSGO and see no hiccups or fps drops.

I'm using MSI afterburner (can be used with any vcard) which is good for auto fan, overclock (don't need it so far), video record, fps/cpu/ram usage monitor. But also because it brings RivaTunerStatisticsServer which allows you to set your max fps in any game you add as profile and avoid overheating or excessive use of the video card.

So long story short: I'm playing on 1600*900 (desktop and game) and also use windowed no border to get the same view as fullscreen and I set fps in RivaTuner to 65 max. (maybe if you don't want that program use command fps_max 65) I don't use full screen because it causes screen tearing and enabling v-sync is bad cause of input delay.

Don't forget to use in your config these commands: cl_forcepreload "1" and sv_forcepreload "1". The trick is to use an fps limiter. But you won't get miracles in maps like insertion and the new ones, but in dust2, nuke, mirage etc you won't notice fps drops even on pub servers with 32 people.

In the launch options of csgo in steam library use: -novid -windowed -noborder -nojoy -high (to play windowed no border you need same desktop and same game resolution to emulate fullscreen mode.

Lastely, go to cfg folder of csgo and open video.txt (after you chose your video settings in the game) and make sure this is as follows: "setting.mat_queue_mode"	 "-1" That's one of the best options to make sure you don't get fps drops. Then set the file to read-only in properties.

Lastely no2. Make sure your cpu cores are unparked.