I just tried the new version of the FR3,5 and will copy paste my post I made at the studio397 forum here.
First of all, make sure you have the correct version of the car selected.
When you join an online server it will most certainly be running the old version.
The new version is 1.6 and you need to subscribe to it from the workshop and then select the correct version in rFactor.
(You can notice that you are on the correct version, when you are still on DX9 the lights on the steering wheel will be very dim and on DX11 they shouldn't be that bright any more)
I just tried the new version on the Barcelona circuit and had a race there with the old version yesterday. So I have direct comparison.
What I noticed was that the in the Car Selection Tuning setup page you can now select the Roll Center.
Now regarding the FFB, it has changed slightly. (I have a t300 and optimal settings are now multiplier 1,33)
What is most noticeable for me is that when you go through fast corners, and your tires are overheating, your FFB will get lighter because you are loosing grip. This is very noticeable on the default setup, if you reduce the front and rear roll bar quite a lot you will have more grip and this effect will be less, since you have more grip.
The car now feels much more alive through slow corner sections where there is now downforce. Those corners used to be super tricky with this car because the steering FFB was almost 0.
Overall I like the update, it is now more noticeable when the car is starting to oversteer and it is much more enjoyable when there is no downforce pressing the car down.
For this quick run I used the default setup and only slightly softened the Roll Bars and increased the Caster to have more grip in the high speed corners.