I don't think GTR3 will do well tbh. Those guys are barely related to the old Simbin (which are now split up between the people making Raceroom and PCARS). I don't think the sim racing world is big enough for 2 dedicated GT racing games, and Kunos will surely have the upperhand with physics. Graphics wise it's going to be equal as they are both using UE4. Feature wise there's really not going to be too much difference either as they are portraying similar series.
I actually heard that Simbin now consists mostly of freshly from university graduated young people. Don't know if it's completely a good thing or not