My English is quite poor so I try to make this as simple as I can. I'm trying to get as close as possible to "real time" gaming (FPS games). I mean I'm still having that "die without seeing enemy coming from behind a corner" crap oh and the "rubber bullet" effect. Even 100+ pingers see me before I see them. I have done all kind of "fixes" I have found from "fix lag" sites but so far nothing helped. Also I still have stuttering and fps drops (graphic settings are lower than ultra). I have also opened all the necessary ports (Firewall rules)

So here's a thing I'm not yet familiar with:

TCP Optimizer: "You can use MTU size 1500"
- 1500 set

CMD prompt:
- ping using MTU size 1500: "Packet needs to be fragmented but DF set. Packetloss 100%"
- MTU size 1447 gives a reply from the pinged address. Packetloss 0%
(CMD prompt: C:\WINDOWS\system32>ping [selected target address] -f -l 1447)

But this happens when setting up different MTU sizes in the modem settings.
MTU size 1447 vs 0 (default)
- MTU 1447: ping 10 - 15 ms, dl speed 85-91 mbits (speedtest.net)
- MTU 0: ping 5 - 8 ms, dl speed 95-97 mbits (upload speed, 5.11 mbits, doesn't change whatever the MTU size is)
- on a certain game server my ping is normally around 45. When changing the MTU size in the modem settings (0 -> 1447), my ping increases by around 15 ms.

So what should I do with the TCIP MTU size and the modem MTU size? And can this MTU thing cause problems??

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Here's the specs of my gears

64 bit Win 10 + anniversary update (all the unnecessary services are disabled and unwanted apps deleted)

100/5 mbits cable Internet connection. Using wired connection. Wifi is off.
Cisco EPC3928 cable modem

i7 6700K @ stock speed (up to 4.2 GHz) (temp in heavy load around 60 C / 140 F)
Gtx 980 ti SLI (temps in heavy load around 70 - 75 C / 158 - 167 F
M.2 SSD
16 Gb RAM @ 3000 MHz
Gigabyte Gaming 7 mobo + the latest BIOS with stock settings excluding the RAM XMP setting
1000 W PSU
100 Hz 3440x1440 monitor
Razer Orbweaver keypad + Steelseries Rival 300 and Corsair M65 RGB mice (native DPI / 500 hz)

All the drivers and stuff are up to date. No beta level stuff.

Please I desperately need your help to solve this everlasting struggling. Thanks in advance.