...can't tell you how many additional channels that translates to, but I'd guess between 2 and 4 times as many. So, it's really more a question of how *big* you're willing and able to go.
With a 120cm, you should get most DVB with a 3/4 or less FEC ratio at 58W, 72W, 89W, 91W, 99W, 103W...