T-34-85’s top speed is 55km/h, its reverse speed is 8km/h, and it’s HP/Ton is 15.6.
M4A3’s top speed is 42km/h, its reverse speed is 5km/h, and it’s HP/Ton is 15.2.
The T-34-85 is a clear winner, with its most noticeable features being the top speed and in some cases the reverse speed.
Moving onto the gun handling, the T-34-85 has 25 degrees per second turret rotation speed, 4 degrees per second vertical targeting speed, and -5 degrees of gun depression.
The M4A3 76 has 21 degrees per second turret rotation speed, the same 4 degrees per second vertical targeting speed, and a much better -10 degrees of gun depression.
T-34-85’s turret traverse is better, allowing it to be more useful in CQC, but the M4A3 76’s gun depression allows it to play hull-down on a lot of hills.
The T-34-85’s armour is decent for 5.7, but starts to become obsolete past 6.0, though it can use its rear (like the IS-2) to act as armour such that APHE prematurely detonates and gets absorbed by the radiator, transmission, and engine. The turret ring also gets hidden as a result:
The Sherman’s hull armour is less usable, even when angled, and can’t use its rear as protection since the transmission is in the front, and the rear is also angled:
Overall, the armour of the T-34-85 is a lot more useable than the M4A3’s, but it’s not extremely good.
As for the weaponry, the T-34-85’s gun, the BR-365 round has 164g of TNT and very good angle pen, with 71 degrees until chance of ricochet being 100%. However, you can only reload at the quickest of 7.4s.
The M4A3’s M62 round has only 63.7g of TNT, considerably worse angled pen, but better flat pen. However, this gets compensated by a 5.9s reload, which is a lot better than 7.4s (1.5s faster).
M62 @5.9s would be better for Panther Fs and for dealing against multiple targets, whereas BR-365 @7.4s would be better against most other targets, also dealing more damage in the process, though it may struggle more with multiple targets and missed shots due to the reload.
Their firepower is more of a side-grade.
As for the gimmicks, the Sherman gets a 50.cal and a very useful low-speed stabilizer.
If the sherman didn’t have access to these two gimmicks (especially the stabilizer), I would say the T-34-85 would be better in most, if not, all cases (other then when fighting over hills).
Let’s say they are relatively equal, and so giving the T-34-85 that stabilizer definitely warrants a 0.3 BR increase. Hence 6.0. But would a 0.7 BR difference to the M4A3 make sense?
The T-34-85 (STP) also gets (only) two barrel smoke grenades on its rear, which is definitely helpful, but I wouldn’t say that warrants a 0.3 BR increase too.
So you have the stabilizer, two barrel smoke grenades, and BR-367, which you say…
is a skill issue for it being called a side-grade.
Well let’s look into it closer:
The standard M62 shell does pretty decent at angles, though it’s nothing crazy.
It can penetrate flat angles rather well too.
The BR-367 shell effectively is a better M62 shell, doing better against weak angled plates.
And also does better at flat angles too.
The BR-365 shell, however, is quite remarkable against weak angled plates.
But can suffer against thicker flat plates, like the Panther F’s.
So the BR-367 is better than M62 in every way (though it’s nowhere near M82 shot’s 185mm flat pen, angle pen, and 137g of TNT), but it has much worse explosive filler (77g instead of 164g) than BR-365, and has worse angled performance… for better flat pen.
I’d say that’s a side-grade.
So if we have a T-34-85 with a stab, side-grade APHE (to BR-365) and two rear smoke barrels, I would say it would be a strong 6.0 but a relatively weak 6.3.
Assuming the stab is worth a 0.2 / 0.25 BR increase, the smoke barrels are worth a 0.1 BR increase, and having access to said side-grade APHE is worth 0.1 maybe 0.15 BR increase. Totalling around 0.40 / 0.5 BR increase, or 6.1 (rounded down to the BR of 6.0) or 6.2 (rounded up to the BR of 6.3)
Could really go either way but I wouldn’t say it’s better than the T20, which is 6.3, and has the same top speed as the T-34-85s, but an actual usable reverse speed (18.7km/h), better acceleration (16.8 HP/ton instead of 15.6 HP/ton), much better reload (5.9s instead of 7.4s), gun depression (-10 instead of -5), 50.cal, and the 24 degrees turret rotation speed (1 degree off from the T-34-85s).
It loses out on the better shells, smoke barrels, and armour (though the latter two aren’t really important if you have the gun depression and reverse speed to take cover and get out of most situations).