These huge screens will be an attraction unto themselves and a big upgrade for the fan experience in both arenas. That said, I think fifty feet wide may actually be too big for arenas this size. I've seen Montreal's massive screen (30'x17') in action and it's great -- but from some locations it can be overwhelming and distract from what's happening on the ice.
The Pacers main display will be 50 x 21 feet on the long side with smaller 24x15 screens on the ends. Built by ANC, with 6mm resolution on each side. (Here's a press release.)
Here's a mock-up of the Tampa Bay Lightning video scoreboard, which will be 50x28 feet on the long side and 16x28 on the ends. Also 6mm, built by Daktronics. (Here's a press release.)
Oh, and the Blue Jackets are getting a new video scoreboard too. It will be called the "Dispatch Media Center" and measures 25x15 feet.