It depends on what Picture mode I use. I keep it well below the halfway mark on all modes because it's just too hard on my eyes if it's set any higher. For Pro, Movie, and Standard modes, I keep the contrast between 25-40%. I would just set it by eye and keep it at or below the halfway mark. If it's set too high, you will get what's called "white crush" and will lose a lot of detail.
FYI, it's a good idea to keep the contrast setting low because you'll overdrive the CRT if it's set too high and will shorten the lifespan of it.
FYI, it's a good idea to keep the contrast setting low because you'll overdrive the CRT if it's set too high and will shorten the lifespan of it.