Have you checked that you and your friends have similar setups? Do you have a Widescreen TV and your friends have normal 4:3 TVs (this affects camera fov and thus performance)? Do you use different resolutions (1080i/1080p, 720p/720i, 480p/480i)? Interlaced screen also usually looks a bit more laggy than progressive, and different TV-technologies produce different amount of perceived lag (overhead projectors are usually pretty bad for any games that require lightning fast reflexes). Also check that you are using correct cable to connect your console to your TV. If you have different options, it might be a good thing to test them all (for both performance and image quality improvements).