I'm not sure if they would since they're in teams which can make them look better than they really are because of the more defensive systems they play. Gibson, especially, since Boro were such a defensive-minded unit. He might fit Man Utd's backline though, because he's played under Karanka, which I suppose is like playing under Mourinho with much, much, much, much cheaper parts.
Anyway - on Van Dijk - does it not concern anyone that he comes from a team that played a very defensive system under Puel and yet when he played this season, his team still managed to concede 23 goals in 21 games? In comparison, when Matip played, we let in 26 goals in 28 games, and that record was 31 goals in about 28.5 games with Lovren. Of course, these numbers themselves don't really mean much, but then, if we consider the context that we play a very much more open system than Southampton do, were forced to change our CB partnership several times due to injuries and the Matip/Cameroun fiasco, play without a defensive midfielder, and use a makeshift leftback, then these numbers do raise a bit of trepidation in me that we're walking into another Southampton trap.