The G is the serial upgrade to the F series which had some of its final run upgraded with the 75mm long, to create the F2, which later were renamed to the G.
Its effectively the same tank with a number of evolutionary upgrades. According to Doyle & Jentz, the G production ran from Apr '42 to May '43.
The G Model in game reflects the final variant from May '43 with most modifications listed in the book present, possibly with the exception on the following:
The vision slit ports on the side of the hull next the driver and operator were deleted between April and October, and the turret vision slits deleted on the left turret front - in game the reverse seems to have been modeled as the right vision slit on turret is removed, and both hull slits are present.
The 30mm front plate being welded on as opposed to being bolted on, which occured from Apr’43 and
The replacement of the 75mmL43 with the L48 which began in production runs from Apr '43, along with the addition of Schurzen against ATRs.
In addition the Ausf G game variant provides you with an additional 20mm of “spaced” armour via the attached track elements, which generally take a round or two depending on caliber before they’re shot off. So more armour by way of 30 mm of welded plate and 20mm more for at least the 1st shot via suspended tracks.
Gun performance and MG performance will be identical to the F2, which is to say effective at range against all Soviet armour in game. The point made earlier WRT the PzIII N 75/L24 Gr.HL/C (HEAT) is valid, as its less susceptible to RNG, at least in the current patch, than the PzGr. 39 of the 75/L43, particularly against the KV-1 and the UFP of the STZ.
It’s also worthwhile noting that the source suggests that many crews would take the Gr.HL/C round instead of the SprGr HE round because it still produced satisfactory HE effects and could also be used against tanks, although its noted that it was not as effective as the PzGr 39 in that role. Whilst the devs have removed this round from the PzIVs to make the PzIII N viable in game, technically the round was available to both.