You’ll see this comment all over here, 10 bit SD is hardly ever more useful that 8 bit, except in a few rare instances. 10 bit is a waste of drive space.
Yes, you will get better graphics when you render to 8 or 10 bit, why your footage is getting softer could be a scan line problem, 480 going to 486, you want 4 extra lines on the bottom and two on the top. Otherwise it could easily look softer.