The 76 mm offered around 40-50% better penetration at 500 m than the 75 mm. Superiority improve marginally as the range increased (heavier round traveling faster). It also offered easier aiming, with a flatter trajectory and lower flight time.
Typical penetration figures for the 75 mm at 500m and 30 degrees are 60-70 mm with AP/APC and 75-85 mm with APCBC, depending on source and tests.
Typical penetration figures for the 76 mm at 500m and 30 degrees are 92-100 mm with APC and 98-105 mm with APCBC, with the same caveats as above.
HVAP, which was in limited supply and limited issue, gives 140-150 mm at 500 m, same conditions as above.