I've done exactly that... set it to 720 deg. of turn. It does take a bit of getting used to but certainly offers greater realism. Last night I did notice my times slowly becoming a bit better.
Wanted to give some feedback regarding this issue I had...
I had been struggeling with the 720 deg. of turn because I lost about 1 second on my laptimes in Blackwood when switching from 200 deg.
After having tried for a couple of weeks I decided it would be better to switch back to 200 deg. again and uninstalled the Logitech drivers.
However the experience was downright awkward. And immediately I missed the sense of realism with 720 deg. of turn so I switched back to 720 deg. again.
At that point I thought I should try a custom setup from one of the more experienced people. I found "racer's" setup and am using that now on Blackwood.
Worked miracles for me as I recently did a 1:07.940 on Blackwoord. I'm currently 12th on LFSWorld. What a wonderful game!!!
You just need some time to practice with G25 and you'll become as fast as used to be.
After a few months with 720* lock, H-shifter (CL obiously ) I'm justa tenth slower than I used to be with 200* lock wheel and paddle shifting (CL too though)
Just keep in mind that when you've selected a car, in the garage in the steering menu you also have a wheelturn setting at the right of the screen. Don't adjust that one. If you are in a GTR it will be set to 540 but if you change that one to 720 you force the car to a default 720 making the steering way too indirect. Once you set the wheelturn in the control options you dont have to change it anymore. In the setup its just there for reference so you can see what wheelturn that car should sync to.
Atl east that what I figured was your initial error when you said you changed 540 to 720. That can only have been in the garage provided it was then synched to 720+