It seems like Mafia II has an Extreme difficulty that may be unlocked at some point in the future.
In pc\sds_en\text\text_default.sds, there's a file called TextDatabase.dat. Within this file is a listing of the difficulty options and their descriptions:
00_59_03_0000:Difficulty 00_59_03_0001:Easy 00_59_03_0002:Medium 00_59_03_0003:Hard 00_59_03_0004:Extreme 00_59_03_0006:This option is suitable for beginners or newbies who do not play shooters very much. 00_59_03_0007:This option is suitable for most players who are already familiar with action games. 00_59_03_0008:This option is suitable for skilled players who enjoy a challenge. 00_59_03_0009:Think twice before using Extreme level. It is difficult even for experts or highly experienced players.
You can unlock this feature by Extreme Level Difficulty mod.