Don't know if this was mentioned before - no matter, I found something...
Edit: all maps, Insurgents/Security, online and local
When joining the action after the truck drive, going into settings and change the effects quality value from "high" (or medium, very high) to low - apply - changing back to the start value "high" - apply - and going back into the game then the graphics performance increases instantly - in my case - by 15 - 25% (it's map depending).
Edit: the settings change can be done at any time within the game, even in the preparation phase or during truck ride or death cam...
Typically the game starts at 45-50 fps at 99% graphics load, when making the changes as decribed above I'm at stable 60 fps as desired and approx. 80% load which gives enough head room for action loaded situations.
No other quality settings change has this effect.
Probably other interested players want to try this out to confirm or refute this finding. Maybe it's just my config.
Playing at 4k/60 fps.
CPU...........Intel i7 5820k @ 4.4 GHz (44x 100 MHz, 1.291 V)
Board........ASUS X99 deluxe (BIOS 3902)
Graphics...ASUS Strix OC 980 4Gb (CC 1525 MHz, VRAM 3900 MHz)
Memory....G-Skill 32 Gb (4x 8Gb @ 2400 MHz)
Storage.....Samsung SSDs 850 pro
Windows 10 pro 64bit
Nv419.67, Nv425.31, Nv430.39
Frame Rate Limiter @ 60 fps in display driver via Nvidia Profile Inspector