Using a T34/85 to kill Panthers, Tiger 1's, Firefly's is relatively easy in our current combat environment, you ambush them. That in and of its self is not due to the "uber" capabilities of the 34/85, but is a result of the tactics. My personal nemesis is the Jagdpanzer I70, and specifically one with 27th driving it, lol. Between the tanks impressive capabilities, his knowledge of its strengths and weaknesses, and his ability to see you where ever you are, makes it a daunting task.
Be careful increasing the perk cost of the 34/85, many gv'ers say they will leave if they increase it. You could lower the cost of the other perked tanks, to bring everything "back into balance", what ever that means. It really depends on what the objective overall is, if it is to reduce the usage of the 35/85, that's not going to happen. If it is to increase the usage of other tanks, then change their perk cost.
As a side note to this discussion, it is interesting to note, most of the comments for the increase in perk cost of the 34/85, are coming from players that don't even gv the majority of the time.