I had quite a good time at the US Army Armor Center Library and Armor Museum at Ft Knox each time I attended an NCO Development Course there. Twenty years in the US Cavalry. I also have 'quite a few' books on Armor. Some notes on the Sherman
ease of production, ease of shipping, mobility, reliability, Infantry Support and 75mm cannon for the HE round
Correct, the JUMBO was the breakthrough tank, to break through enemy forts and AT defenses. The lead tank to reach Bastogne was a Jumbo named Cobra King, a fairly new to service unit. Then fitted with the 75mm.
During March and April the JUMBOs in Pattons' 3rd Army got upgraded to 76mm gun. Cobra King also had a .50 cal HMG fitted coax instead of the .30 cal MG. Shortly after this refit, March 1945, Cobra King was the command vehicle for the Ill-Fated Raid on Hammelberg. It was damaged and abandoned, recovered by (edit) ??? when ???? and stored at Hammelberg....used as a "Gate Guard" display vehicle for years at Vilseck, pedigree unknown.
In 2008/2009 it was established that this was all the same tank, making it quite historic and it is getting a full restoration. It has been refitted with a 75mm weapon in it's Bastogne-era fitment.
By today's standards of gunnery, WW2 accuracy was poor. Often 2-3 shots to get a hit at 1000m, Hollywood movies be damned! Yes, 6 or there about ready rounds is not a lot, other rounds are not far away. And remember, the US and the Soviets greatly outnumbered the Germans. Fire and maneuver, the German tanks were vulnerable to flank shots as noted. Also, the German tanks did not like US Artillery or air power, no need to go rushing in once German tanks are spotted. The Sherman was adaptable, had the internal volume to support modifications and upgrades, not the case of the T34