Three words: told you so :)
152mm gun-launcher (the weapon used on Sheridan, just without the option to fire Shillelagh missiles) in the XM551 (Sheridan prototype) turret and T49 hull.
Top gun: 152mm Gun-Launcher XM81
Penetration: 76/152,4/76 (HE/HEAT/gold HE, gold HE shells have larger blast radius it is assumed)
DPM with HEAT: 1825
Aim time: 4s
Hull turnrate: 44
Weight: 22,234 tons