@BenganJ
Sheesh relax, I'm just experimenting
Done some more testing now to see if Multimon affects performance. I went to Las Vegas (cause usually it lags pretty bad for me there) and tried without and with Multimon.
The camera is facing towards the city. My truck is in the Volvo dealer.
Settings are all on Ultra, Shadow texture size is 8192. My FPS was sitting at about 92 to 80 with some traffic around. This is without Multimon.
With Multimon, same FPS.
Now I tried to see if it increases or decreases FPS in my truck's interior.
Both have the same result: About 60 FPS and lower. Lowest was about 51. I turned down the mirror distance to High and the shadow texture size back to high (which is 4096) and got over 70 instead.
So basically, I recommend anyone who sees this to
keep Multimon. There's no point in removing it at all.