At first, I'd say that you'd want a 55 gal + tank for sure. But, it depends on what you want to keep with it.
When I kept my first redbreast (caught him at 2''), he went into a 46 gallon with a bunch of spotfin shiners, a 1'' bluegill and a 1'' green. After the redbreast reached 5 inches (the other sunnies at 3''), it was like a switch turned on. It killed the bluegill and the green, and constantly chased the shiners. The shiners were also 4'', and could get away, but they constantly were harassed. So, a 46 gallon was fine if you ONLY want ONE redbreast. But if you want several, I'd say 55 gal minimum, but a 75 gal with a larger footprint would be better.
As a side note, I have kept redbreasts since then with better results. I kept 4 redbreasts and 2 greens in the same tank. They were crowded, and couldn't really set up territories. But they simply got too big for the current tank, and I didn't keep them long after sexual maturity.