The T-34/85 and the M4A3(76) are very close in gun, armor, and other specs, there are of course differences but nothing like some folks seem to think.
As for the 76mm Sherman gun, it could do @116mm of armor at 500 yards with APCBC ammo and could kill a T-34/85 frontally. The T-34/85s 85mm BR-365 APBC round would do @111mm at 500 yards and likewise could kill a Sherman. Both tanks offered @ 100mm of actual protection frontally, the T-34 with 45mm of armor sloped and the Shermans 51mm of sloped armor, giving both tanks approx 100mm of protection (give or take). Certainly at ranges greater than 500 yards, the rounds would often not score a kill if they struck the front armor. Armor is designed after all to protect the vehicle otherwise all the tanks in WW2 would have just been canvas covered trucks with guns on the back. The special tungsten based ammo that both tanks had from 1944 would of course do better, US HVAP (not included in AH) would do 200mm of armor to the Soviet 85mm APCR (which is in the game) 140mm of armor, and thats at 500 yards (0 degree slope).
M26 Pershing vs T-34? well the M26s armor is vastly better, and so is its gun, any specs will quickly indicate that. The M26 is a heavy tank.
Some of the best books out there are Ospreys "New Vanguard" series on specific WW2 tanks. Lots of great info, sans the nationalistic BS and half baked crap that are in a lot of posts and some web sights. Not that its going to do any good, cuz dumb myths and grossly exaggerated statements are almost unkillable imho. If it can fit on a bumper sticker it usually wins out over real info, every time.