The guy who sold me the TV said " My mate was using composite until I switched the lead over for him to HDTV lead and the difference was amazing" Maybe general sales BS or he was right.
If he was using composite and switched to a HD cable then he would notice a difference. If he was using component I doubt he would have noticed much of a difference

Composite and component are two different types of cable.
Component = good
Composite = bad

