Suited Connectors

It has been said that a 5 6 suited connector is better than a suited 5 7 but I somehow doubt that.
Example:
If the flop comes 3 4 K. Then the 56 suited connector would have made an open ended straight. However the chance of that occuring is the same as the flop showing 4 6 K. In that case, the 5 7 suited would have made an open ended straight instead of the 5 6 suited connector. The chance of 3 4 K occuring is the same as 4 6 K.