> how much faster would a non-Windows machine have to be
Until Macs run games, it's a pointless comparison. If Steam did for Macs what they did for Linux, then we'd have something interesting to talk about. But a PC without games is about as attractive as... a Ferrari, I guess. If somebody handed me a free 200K$ sports car, I'd just sell it. It's useless for my lifestyle. A PC that can't play games is equally useless to me.