here is the math if you add mark target
PZIV finishing off a T-34/85: (800/160)*5.825/(88.7097%)=32.8318sec
T-34/85 finishing off a PZIV: (640/160)*8.575/(68.75%)=49.8909sec
T-34/85 finishing off a PZIV plus Mark Target: (640/160)*4.2875/(68.75%)=24.9454sec
Correction
Mark vehicle gives 50% more damage not 50% reduction in reload time. Therefore, it should be:
160x1.50 or (640/240) x 8.575 / (68.75%) = 33.2606 seconds
But (640/240)= 2.667 so we have to round to 3 shots the and figures will be:
3 x 8.575 / (68.75%) = 37.4181 seconds
In that scenario 1 t34/85 cant beat 1 panzer4 even with the help of mark vehicle.
Solution
I think making the t34/85 cheaper or a single call in are all nice things to have, but the one thing that is badly needed is a penetration increase. If penetration is increased from 110 to 160 it will become a match to panzer4:
T-34/85 finishing off a PZIV: (640/160)*8.575/(100%) = 34.3sec
And this will enable 2 t34/85 to stand a better chance fighting the less expensive Tiger call in.