We took the plunge and have separated the two boys so that they have their own bedrooms. Bright Eyes has been so angry with his brother that it was becoming impossible for them to be together.
I think I assumed that the anger would disappear once the rooms were fixed, but of course, it didn't. He's just angry. He does like his room though - he's calling it 'the lab' and has a sign on the door saying, "Mad Scientists only. No brothers or sisters allowed." I think his big sister wrote it for him.
I have to remember that for once, I didn't do this change for him. I did it for his little brother who definitely needs his own space and place to develop his own personality away from Bright Eyes' domination.