I don't play GP4 with that wheel, so I can't help out with a file. But I have the wheel, too, and the most important thing is to decrease the steering lock from the original 900 degrees to 250 for realistic F1 car behavior. I assume you have the Logitech driver and Profiler? Use the profiler for a new GP4 profile and test a bit with various settings.
GPGSL : Team Owner of 'Maverick Track Performance' (MTP)