Gun performance about equal.
AP+ on the Allied 76L51 better than the AP+ on the German 75L48.
Pz IVH = much better sight and optics, in terms of both quality and design.
Tony Williams - I've got some interesting documents you may want a look at...it's a 'tactical primer' for 75L48 AP+ vs. the mantlet of the IS-2 and IS-2m issued to German AT and Pz gunners late in WW2. Apparently part of the mantlet was a 'weak spot' at cloer ranges using tungsten AP with the 75L48. As soon as I get home and near a scanner...
Overall the 76L51 armed Sherman is a little better than the Pz IVH I'd say. Better mobility, a little higher silhouette but once you have the cast frontal hull Sherman with the 76L51 (i.e. M4A3E8) the bottom line is that a M4A3E8 has a noticably better chance of surviving a frontal 75L48 hit at 1000m than the Pz IVH has of surviving a 76L51 hit at 1000m.
If rarity matters at all, the first Sherman modeled should be the M4A2 with the 75L38 MA and the first T-34 modeled should be the T-34/76C. Then you'd have the most common 75/76mm armed MBT for Germany, UK, USA, USSR.
Mike/wulfie
p.s. Yep Tony the 17 Pdr. was a real hot one. Pz training manuals from 1944 onward instructed Pz gunners to engage the lone Firefly of a British Sherman troop first in any/all engagements.