I was tweaking around with my Settings a long Time, and all I can say is, that in my Case it has something to do with the Graphic Settings.
What I have found out:
When I fly a Campaign-Mission at Dusk or at Dawn or at Night, the Game runs smooth and liquid as never before. Even with Medium Air Activity in 1918-Campaigns. But if the Sun rises up during a Mission, the Game begins to Stutter... I don't know why and I don't know how, but I've seen this Effect now several times, and it's always the same. It has nothing to do with my CPU, that is for sure. It must be something that I must tweak in my Graphics-Driver, it is some Problem with the Shaders IMHO. Unfortunately I am also not able to run the Game with the Default Shaders (Runtime.dll Crash every time), even after a fresh Re-Install. My GPU is an NVIDIA Geforce GTX 970 and my OS is Win10.

I've tried so much different Settings in the last Months, but nothing helps.

And if this was not bad enough, I have found out that WOFF 3 runs even more worse on my System than WOFF 2. I don't know what to do anymore. Very Sad!

But as I said, I am pretty sure it has something to do with my Graphics-Card. Will not give it up...