Game "boss" question TGEA & TGE

I have a question about in game bosses... sorta..

My idea is, that in an enclosed area (like deep in an interior map) where nothing outside it rendered, lets say you have about 10 - 15 player characters and you come into a boss room.. I know its graphically client side, but just for arguments sake, you have a very hefty server uber capable of handling everything its supposed to..

So, what is the MAXIMUM poly-count you'd try an pull of and not ruin the game.. I think a great deal can be done with normal maps to tweak out a low poly model, adn I'm in the process of that now..

But my real question is, if you throw a 1024X1024 textured creature with 10000+ polys can you get away with it?

Thanks - Ron