Well most of the streamers doing that have cranked down to 800x600 and put all the settings as low as possible, does it 'help' no because even if it shows 500FPS (which I would call BS on recorded not live and even if live, very easy to put a 'mock' FPS on your screen overlay). What is the point? other then whipping out '$%^& sizes' and saying I am bigger.
Do be aware, that when you have higher end hardware, as you do, you hit a point your inversing the problem. That is to say, while on lower end hardware lowering the graphics (always do that FIRST) then the graphics you increase FPS, but with your type of higher end, you hit a point that actually your causing FPS loss then gaining it. Because your trying to force the hardware to do something it isn't really meant for (low resolution, low graphics) it actually works twice as hard to force itself to be 'bad' .
Now to ease your point, since your insisting, do these basics and post some replies on each one and let's see if you eliminated any other 'hidden' things going on. And BTW you can't "pad" your FPS to avoid say upclose 20 other players all at the same time firing rockets and not experience some 'dip' because that is the 'most intense' bit of graphical generating demanded and you hit that 'max'. As long as your staying over 144 (even if you were doing 100 or even 60) your still golden with how it synchs to the LCD.
Do be aware, if your talking about streaming, even the top tier Twitch broadcasters tell you the same thing, expect a 50% drop in FPS no matter what, but since your getting 200FPS anyway your dropping down to 100FPS still doesnt' matter your way above any needed level anyway and won't affect your actual game play. Drops your hearing and seeing people get upset is dropping to 20s or 30s because we all can't afford a expensive mega rig like yours.
But IMHO I think your looking for a problem that doesn't exist at all.
Did you install all Windows Updates? Including OPTIONAL except BING? Check them and repeat till ALL are installed.
Download and run Slim Drivers, install all the latest updates but you don't need to reboot until you do the last update
Go to www.filehippo.com download Malwarebytes do a CUSTOM scan, set it to scan all your drives, this is NOT a default setting. Additionally AV doesn't pick up alot of malware - this resolved almost ALL other similiar posts to date as most had Malware the AV didn't pick up.
Remove whatever AV your using and and download AVIRA, AVG, Comodo or Panda and do a CUSTOM scan, set it to scan all your drives, this is NOT a default setting - this repeatedly has resolved alot of people issue relying on MS Essential, or had a version of Norton/McAffee that either expired or just /old/ interfering with gaming due to how the engine works.
Repeat the AV/Malware scans till the system comes up clean.
Download and run SPECCY, copy and paste the first tab to show your idle temps
Download and run MSI Afterburner, go under settings and enable On Screen Display (OSD), then go through and enable what it will monitor. make sure to set those things (RAM, Temp, etc.) to SHOW OSD so you can see while playing in game what is going on in your system.
As we want to just /test/ what is up, play not only GTA V as you had been but other games and compare. Do you see anything funny that the CPU or other parts are maxing out, high Temps, etc. Test by playing different save points like one where things were very busy / intense (helicopter many vehicles etc.) then when it is quiet (sitting in your room for example) Do you see this 'FPS' problem when in SOLO MODE? Only when Multiplayer?
Open Computer, Can Air dust out the bunnies and use paint brush on the vents, coolers, fans, etc.