An update, if anyone's interested.
I've settled on the settings recommended by Fanatec, but changing NDP to OFF and INT to 1. This is a bit harsher, and will oscillate if you let go of the wheel, but provides quicker and more clear FFB. NDP is dampening everything and INT is intrapolating the FFB signal. I understand why Fanatec recommends NDP 25 and INT 3 - it's clear and crisp enough but safer than NDP OFF and INT 1 (it's softer and won't oscillate).
I don't notice any difference between LIN and PEAK, except that LIN is much weaker. So I'm sticking to PEAK.
There's zero reason to fiddle with the other settings if speed is your primary concern, no matter what some youtuber shouts at you. However, if you want to feel something else than what the game developers have intended, go ahead and fiddle. It's like using an equalizer when listening to music. I just want what the game developers intended (I also use neutral sounding speakers/headphones at home for music).
In-game, with 8 Nm, I use 1-1 with high downforce cars and 2-1 or 3-1 with road cars. That's simply what I'm quickest with and find it easiest to be consistent with. 5-1 in-game and 100% FFB, with 8 Nm and GT wheel, is for impressing friends and feeling manly on forums. With a heavier and bigger wheel however, that force will most likely be needed with road cars.
Only occasionally something happens on screen that should be felt in the wheel but isn't. This has to be entirely the fault of the simplistic FFB in GTS. Otherwise, everything that happens and affects handling is felt extremely clearly in the wheel. There's no rumbling, vibration, cogging or whatever except for this - perfect smoothness.
I wouldn't complain if the FFB is completely unchanged in GT7, but sure, I wouldn't mind an improvement.
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If anyone's using the desk clamp, pull the wheel upwards toward the ceiling when tightening the last bit. That will prevent flex vertically. Horizontally there's no flex.
The QR1 Lite is perfectly solid and quiet as well.
And if you bolt your desk to the wall, there's zero flex from anything - you get perfect silence and clear FFB.
Use zip ties on the pedal plate and a strap through those and around your front leg of your office chair to stop it from moving.
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If I'm mistaken about something, please tell me. And if you have further advice, please share!