Crossfire isnt a big game with low fps with a super nice computer like that. I have a horrible pc $300 laptop I run 20-50 fps. With that you can run as many as you need but not something ridiculous such as 30, that takes lots of ram but you can possibly fit almost a full room, I say a good start would be around 10 people. You can experiment with it since crossfire has a strong tendancy to crash a lot.