TemplarGFX's Impact FFB heavily modified for T300. All credit to him.
Set all the wheel gain settings to 100, except Auto Center, which is controlled by the game. Rotation to 900. Set all the FFB values in-game to 100 and soft lock on.
Extract the "forcefeedback" folder in this ZIP file into the game's installation folder (example : c:\program files\steam\steamapps\common\Dirt Rally)
Extract the "forcefeedback" folder from the "Originals" folder in this ZIP file into the games installation folder
While FFB is a highly subjective matter, I think I managed to hit some sort of a sweetspot for T300 with these settings. There seems to be more sense of control, at least for me!
Naturally you may want to tweak in-game values according to your own preferences.
FFB T300_100 v1.01
FFB settings for T300