I personally have a different opinion on the importance of projectile design. The 76mm may have had a lower i.V. but the projectiles were not sufficiently rigid under the nose (a soft spot due to the sheath hardening pattern) to actually sustain higher velocity impact. If the US APG trials are to be believed, any extra energy would be largely wasted on these projectiles as these would more frequently shatter. Notice that the UK used a different hardening pattern (decremental hardening). I refer for further reference to a post ww2 report:
PROGRESS REPORT No.1 ON DEVELOPMENT OF HIGH VELOCITY ARMOUR PIERCING PROJECTILES (dated Nov. 1, 1947) reports:
-emphasized by myselfe3" M62 Caped A. P. Projectiles.
Against 3" homogeneous armor at 30' and 45' obliquity the M62 projectiles from both lots fired showed a tendency to split and break up at striking velocities up to the maximum velocity tested to date, namely, up to approximately 2700 feet per second.
individual test cards:
3" homogenious plate* at 30°obliquity, eight rounds fired:
#1 2423fps, incomplete penetration (dent, back bulge with star crack), projectile split, not effective -ABL
#2 2523fps, complete penetration, projectile broke up, not effective
#3 2549fps, complete penetration, projectile broke up, not effective
#4 2740fps, complete penetration, projectile broke up, not effective
#5 2518fps, complete penetration, body cracked, but effective
#6 2495fps, dented (no hole), projectile broke up, not effective
#7 2627fps, dented (dent, no hole), projectile broke up, not effective
#8 2755fps, complete penetration (clean hole), projectile nose split, effective
result: projectiles split or broke upon most impacts (except #5 and #8).
3" plate at 45° (2 rounds fired)
#1 2487fps, dented (no hole), projectile shattered, not effective
#2 2549fps, dented (no hole), projectile shattered, not effective
result: "projectiles shattered on plate, projectiles could not penetrate the armor at any striking velocity obtainable to date."
It needs to be pointed out that the Ballistic limit for 3" plate attacked at 30° was expected at 2420fps (737.6m/s), so all firing took place at velocities above the VL50. Yet, two dents were recorded 2495fps (760.5m/s) and 2627fps (800.7m/s) and an AB(L) at 2423fps (738.5m/s),.
for comparison, the 75mm Pzgr.39 NBL as established by the same testers on the same prooving ground against Carnegie-Illinouis 5 3/16 inch (132mm) RHA plate at 30° was 2743fps (836.1m/s) with the AB(L) beeing 2543fps against the same target -the projectile always remained intact, whether or not it penetrated or ricochetted off. This projectile was also largely intact in impacts at 45° against 5 1/8 inch (5 3/16 inch in some places) plate at somehow higher velocity.
I´d argue that this constitutes not just a marginal or trivial aspect but a very considerable difference in projectile capability to overcome armor. I fail to see how the 76.2mm M62 could hope to penetrate a 5" RHA plate at 30° at equal (or higher) velocities.
* 3" class B RHA made by Carnegie-Illinois, standart homogenious armor plate (alloywise it resembles a Krupp Q420 type where You have twice as much Ni than Cr) treated to 256BHN
edit: Richard Anderson got it first, sry for stepping in