Plenty of mid sized monsters will do well in a 125 gallon tank. Two questions come to mind...
1) Are you intrested in breeding?
2) What are your personal likes and dislikes?
If the tanks going to be mostly a display tank then pick an assortment of intresting fish that can get along and start aquascaping...
If you want to breed then set the tank up in a more generic manor and stock only those fish that compliment your breeding arangement...
Personally?....If I had a spare 125?
I don't see many Red bay snooks at LFS's and the going price is attractive from a breeding standpoint. once you have a pair..breeding is fairly simple.
Not quite as easy as breeding convicts mind you but then cons are only worth about .25 a metric ton...