Faster re-load time (if you can call it that when using an autocannon) doesn't help if you can't hurt your opponent, and only helps if you miss.
Armor for the BT-7:
Hull Front (Upper) : 30mm @ Round
Hull Front (Lower) : 22mm @ 72°
Hull Sides (Upper) : 13mm @ 90°
Hull Sides (Lower) : 13mm @ 90°
Hull Rear : 13mm @ 80°
Hull Top : 10mm @ 0°
Hull Bottom : 6mm @ 0°
Turret Front : 15mm @ 78°
Turret Mantlet : 15mm @ Round
Turret Sides : 15mm @ 78°
Turret Rear : 15mm @ 75°
Turret Top : 15mm @ 0°
vs. the gun of the PzkwII(F) (the version you mention specifically).
Penetration Data for the 20mm Kw.K. 30 L / 55
Pz.Gr. ( Armor Piercing )
Weight Velocity 100 m 500 m 1000 m 1500 m
0.148 kg 780 m/s 20 / --mm 14 / --mm 9 / --mm -- / -- mm
So, must be about 500 meters to have any hope of penetrating the side or rear armor, closer to hurt the turret of the BT-7. Penetration of the hull front theoretically not possible.
The reverse:
Armor for the PzkwII(F)
Hull Front (Upper) : 30mm @ 80°
Hull Front (Lower) : 35mm @ 77°
Hull Sides (Upper) : 20mm @ 90°
Hull Sides (Lower) : 20mm @ 90°
Hull Rear : 15mm @ 81°
Hull Top : 15mm @ 0°
Hull Bottom : 5mm @ 0°
Turret Front : 30mm @ 0°
Turret Mantlet : 30mm @ Round
Turret Sides : 15mm @ 69°
Turret Rear : 15mm @ 69°
Turret Top : 10mm @ 0° - 13°
vs. the gun of the BT-7.
Penetration Data for the 45mm 20K Model 1934 L / 46
BR-240 SP ( Armor Piercing Ballistic Cap )
Weight Velocity 100 m 500 m 1000 m 1500 m
2.45 kg 759 m/s 43 / 33 mm 31 / 25 mm 20 / 17 mm 14 / 12 mm
Can defeat the side armor at 1000 meters, front armor at 500 meters.
Source linky.The site unfortunately does not have the BT-5, but it had the same gun.
Since the BT-7 can kill the II from farther away (especially with a front shot), I would have to give it the edge in a pure one-on-one duel. But who knows -- if the gunsights on the BT-7 were absolute crap, the II might survive long enough to get close enough.