I have never had my quad core slow down an older game designed for one core. If it actually does theoretically have an impact on the performance, the quad core is so damn fast anyway that you won't notice it. If it ever actually did have an issue, you can set a process to run on only certain cores. I think it's an option called "set affinity" when you right click on a process in windows task manager. We used to do that back in the day for sapien when dual cores were becomming a lot more common. I never had an issue there either, but I guess sapien didn't play nice with a lot of dual core processors.