[excession]

'Went to Showdown % is already a good indicator of how well you can push'

WtSD% is OK but there are two reasons why a hand doesn't get to showdown - villain may be very aggro and so a lot of his hands end with his big bets/re-rasies on turn/river or villain may fold a lot.

You need a separate criterion for 'weakness' (or propensity to fold) as a cross-check to see how 'safe' it is to push.