I have i7 6700 16 g ddr4 gtx 1080ti and its lagging alot. Even the cinematic lagging… I read all the post about how to fix it and nothing work… Please Help me on that
I had same issues at game release, intro lagged heavly and was screen tearing really bad.
My solution for that was to set fps to 30, then lagg decently disapeared for me, game was playble but i wasnt satisfied.
Continued to tweak and test stuff, but lagg came and disaperead.
But everything went better and better after every driver and game update.
Now yesterday i did an clean windows 10 install.
Now fully updated and newest drivers forza seems to work pretty good on full dynamic for me.
I cudnt use dynamic before, so I really beleave i had something installed that might caused all problems for me.
Maybay was an overlay, monitor program or something corrupt in the system for me.
We see now over time, im not gonna install any monitor apps for an while just to test, and then install em one at time.
To use 30fps isnt really an good solution, but game might become playble.
As u have an stronger grafic and cpu 
than me u shudnt really have any bigger issue run this, so i really beleave something in your background in windows is causing all.
Hope u sort it.
I did a clean reinstall of windows 10, and the game is the same as it was before i did the reinstall. I got a i3 4130 gtx 780 8gbram. i can run the game on dynamic 1080p cause i race 2 to 3 races with over 50fps with no hitches but after the 3rd it starts to stutter and is unplayable on multiplayer. I see people with i7s and 1080 ti and still having the same issues im having. i thought i could upgrade to 16gb and it might fix it but people with 16gb+ are still having the same problem. Since about 3 days ago i get a crash when “waiting for cars” like 10 times with no errors just CTD. This is ridiculous and Turn 10 needs to work on this issue right now.
New update today but same problems. its like someone is pressing on pause every 2 seconds or so in the cinematics… I did a fresh install 3 times. Even tried the creator update. I went in g sync nvidia setting or inspector and apply the setting that some tell will fix the problem but same. I have nothing in the background that could explain that trouble.I also stop the gameplay mode and auto recording. All other heavy games works perfectly. I have a 4k monitor and a 4k tv. i tried at 1080p too but still the same. Im really mad about that. 145$ for that broken game and no support for it its is NOT OK!!! Should i ask a refund ??? By the way before you ask i have 2 brand new and tested hi quality intern ssd. One small 120gb for windows 10 and one big 2tb for the games. So its not a matter of drive speed either. I HAve an ALienware x51 r3 with i7 6700 at 4ghz with 16 gig DDR4 at 2666 mhz and an external graphic amplifier with Nvidia gtx 1080ti founder edition in it. My 4k TV and 4k monitor are hi end Samsung product. With hdmi 2.0b and display port 1.4.