Earlier there was a mention that perhaps the extra 10mm between 20mm and 30mm wasn't all that much. I'm pretty sure that this pic should put that to rest - the destructive load of a 30mm was far and above the 20mm.
FYI the 30x90RB was the 190 30mm Mk108 model.
The 30x184B was the Mk 103.
From what little I've been able to deduce it seems the 30mm was 3-4 times more deadly than the 20mm.
....size does matter eh!
****edit**** info included from the next post - thanx MOOT sir!!
"If we compare the values with the few data known from ballistic tests, we have some indications that the factors assumed in the calculations are realistic. The 20x80RB M-Geschoss and the 20x110 (Hispano) HE were rated as about equal; the greater blast effect of the M-Geschoss was countered by the greater penetration and kinetic damage inflicted by the Hispano. They do indeed emerge with similar scores. Also, the Luftwaffe reckoned that it
took about four or five times as many 20 mm shells to destroy a heavy bomber as it did 30 mm rounds. The power relationship here is 3.6 times for the MK 108 and 6.2 times for the MK 103, which neatly brackets this observation."