The Red Army took the threat of German anti-tank weapons very seriously, and the 88 mm Pak 43 remained a reference point for enemy anti-tank guns even after the war. In part, protection from this gun was listed as a requirement for post-war medium and heavy tanks. These requirements allowed me to compare the penetration of the German 88 mm Pak 43 and Soviet D-25T. Turns out, a similar analysis was done using the 100 mm D-10T gun.
This data shows limit of partial penetration (PTP) curves of the 88 mm gun against medium hardness cast armour. It is visualized in two ways. The first has impact angle as the X axis and impact velocity as the Y axis. A curve is drawn for different armour thicknesses. The second graph shows the same data, but with the thickness as the X axis and curves drawn for each impact angle.
From these graphs, we see that the 88 mm Pak 43 is a powerful weapon indeed. At point blank range, it can penetrate 120 mm of armour sloped at 60 degrees (incidentally, the armour thickness proposed for modernized IS-2 tanks in 1944). The IS-4's armour protection (140 mm at 60 degrees frontally, 160 mm at 30 degrees on the sides) also offers good but not perfect protection against damage from the 88 mm Pak 43.
At 1000 meters and a velocity of about 900 m/s, the gun can still penetrate 100 mm at 60 degrees or 130 mm at 50 degrees. These look very similar to requirements for the T-54's armour, making it very clear what opponent this tank was designed to fight.
This data shows the same thing but for the 100 mm blunt nosed AP shell. The penetration is considerably higher. Rather than 120 mm at 60 degrees, the gun penetrates a hair over 160. At 50 degrees, this shell penetrates 180 mm of armour compared to the 88's 150. Unfortunately the graph for the Pak 43 does not show penetration at 30 degrees at point blank range, but extrapolation shows that it penetrated less than 200 mm of armour while the D-10 would penetrate slightly more.
At 1000 meters and a velocity of about 800 m/s the gun penetrates 140 mm of armour at 60 degrees and almost 160 mm at 50 degrees, again keeping a slight edge on the 88. At 30 degrees the gun penetrates 180 mm of armour, making it capable of penetrating both the front turret or the front hull of a Tiger II at ranges where the Tiger II can penetrated it back.
And finally, the 100 mm sharp-tipped AP shell. This shell is not as good as the blunt-tipped AP (same thing is observed with the 122 mm D-25's ammunition as well). At point blank range the gun penetrates 130 mm of armour at 60 degrees, a hair more than the 88 mm Pak 43. At 1000 meters penetration drops to almost 120 mm at 60 degrees or 140 at 50 degrees, still keeping just ahead of the Pak 43. At 30 degrees the gun penetrates less than 180 mm of armour, making it a little riskier to fight a King Tiger head on.
When it comes to the Panther, a more realistic opponent, the 100 mm gun can defeat it at a great range. The upper front plate (85 mm at 55 degrees) can be penetrated at a velocity of about 600 m/s with the sharp tipped shell (a range of over 3 kilometers) and at even greater ranges by the blunt tipped shell.
RGAE F.8734 Op.8 D.249 L.1-6 via Yevgeniy Narimanov.