Ok, so I guess if you took a player from say the late 70's, 80's and asked them to play at the same level today they wouldnt succeed?
Then why did McEnroe win an Atp doubles tournament when he was 48 years old? He accomplished the same thing he did in the 70's and 80's in 2006 as a much older, less athletic version of himself. I would say thats pretty competetive.
McEnroes great rival was Borg, Borg had a few difficult matches with Laver when Laver was in his late 30's, such as this one:
http://www.youtube.com/watch?v=XMfBpkUJeKE
Logic dictates that if Laver can be competitive with Borg at a relatively advanced age, he could have been competitive with McEnroe, and McEnroe playing even now would be a top 10 doubles player.
Prime laver, with equipment etc being equal as any peers, would be close to the top in
ANY era.