i think any CB we sign will need to be quick, agile etc, with the way Gerrard likes to play his full backs so far up the pitch, the CBs will likely need to make a lot of recoveries and close down sprints etc, as well as Gerrard wanting to play "possession" football, which will mean the defenders probably playing higher up the pitch, meaning a pacey/agile defender can recover better from balls down the sides / over the top etc.
I really dont expect us to be signing a Tarkowski type, who although a good defender, isnt really speedy/agile or a recovery type defender.
Who knows though.