Nik I've noticed that even with no mods enabled max lvl skill mana consumption is 4 mp per skill, and apparently turning off skill cooldown gives you a permanent adrenaline rush perk affect (not sure if that was intended like the side affect of unlimited fairies making daggers and pet heart and such also unlimited) but if so nice touch either way
not enabled any mods.
Also, I believe that enabling the skill after prestige will increase the mana, but it hasn't. (I could be wrong, the mana recovery rate feels faster than normal.)
((I'm using google translate, so please excuse my poor English.))