I've got the Hendrix version of Day Tripper with John on backing vocals -- on a release called "Radio One," which I've had since probably 1989. (It's a lot of Hendrix bootleg stuff.) It's been ages since I've listened to it but I recall not being too impressed with Day Tripper -- at least as far as you can't really tell if it's John or not in the background. I may listen to it again tonight though just for a taste.