The limit that is typically recommended is around 25% semolina although I know of a pizza operator who says that he uses 40-50%. Even at that level, the pizza and crust tasted great.
You will get a chewier crust using semolina, but if you let the pizza sit around too long, the crust can take on the quality of shoe leather. I also found that leftover semolina pizza slices don't reheat very well. They get tough and are quite different from the original. So, if you can, it is best to eat the pizza as soon as it comes out of the oven and finish it off entirely.