As of now, the GV set could most stand to see:
Valentine tank. Coveres the widest time-span aside from the Churchill, mounting the 2lber, or 6lber, which would be quite capable in LW, provided it is allowed to have APDS. Is was the most numerically important British tank, and would also give us the base for the Archer SP AT gun)
Panzer III. Primary German battle tank up to late 1942, early 1943. Last action it saw widespread useage in was Kursk, lead the German blitzkrieg across Poland, France, Africa, and the early Russia campaigns. Could mount 4 different guns": the 37mm, 50mm L/42, and 50mm L/60 in Early War, if we get 2 different models, and the 75mm L/24 in Mid War if we got a third model. Would provide the base for a StuG III
BT-7 A major player in EW, and would be capable of dealing with 37mm-armed Panzer III's in EW. Would be slighlty inferior to 50mm armed panzers, and the Valentine.
M3 Stuart. Just something to let the USA compete too. An M8 with more armor, less speed, and another machine gun.
Adding these four tanks would put the Panzer IV F2, and the T-34 into the perk-tank realm, reducing their useage, and letting the others have a chance. The Panzer III could knock out the T-34 out to a range of 300m, and the Panzer IV to over 2000m, Valentine could do so from about the same range, depending on the cut-off date for EW (it needs the 6lber to be a threat to the T-34).