you can find some 10 that are louder than 12. Some speakers are easier to make louder than others, not dependent on size. 12" normally should be louder and can take more abuse than smaller subs if they are spec'd similarly. (same brand, etc)
03 Steel Grey 6MT :shiftdriv
Volks TE37| Eisenmann Race 83mm + section II| RE Rasp Pipe| Vogtland Springs| Kenwood KDC X994| Poly RTABS| many more...