I want to buy a gaming pc with a kfa rtx 2080 super ex, an i7 9700kf and a 240 hz monitor, do you think I can achieve a constant 200 fps?
In low settings over 300fps in full hd
For sure. Even almost 400.
With low settings in 1080p you can do it clearly.
If that's your plan, you don't need an RTX 2080 Super.
I have an i9 9900K with an RTX 2070 Super and its load is at most 65%. This means that if you had a better graphics card, you would get exactly 0% more performance.
An i7 10700K with an RTX 2070 Super would be highly recommended.