There's a guy called Zak who thinks that when you partition a drive, the first partition takes up the outer edges of your drive, while subsequent partitions take up space closer and closer to the centre. This would have the implication that your very first partition would run much much faster than the average speed of your drive, since the data is stored on the outer edges; and subsequent partitions would run slower and slower until you reach your last partition which would run at a crawl since it is situated in the very centre.
He has posted up some Nero figures which seem to support his theory, although he isn't even sure himself if this is at all true. If it is true, then you should store your OS on a very small partition, and your games and applications on the next partition (as small as your games collection would allow). Then all of your other files should be stored on the rest of the drive in whatever way you like. Since the OS and your games/applications are stored on the outer edges of your drive, they should perform at blistering speeds at all times!