divad hit the nail on the head. I do think that a cabintop mounted traveler could impact performance a little. First of all you will probably end up with a heavier boom. This is slightly offset by not having hardware hung on the end of the boom but not completely. The bigger issue is controling twist. I have found it much more difficult to control twist in the mainsail of a boat that has a cabin top mounted traveller. This results in a powering up a little in heavier going when you''d rather blade out to control weatehr helm.