Here's what I think on Ace v. Akainu
I think Akainu's devil fruit, is a more complex version of Ace's and that the properties of Lava, which can't be affected by fire, will only burn hotter when exposed to it
that's just how those logias stack against each other...
in retro-respect here's how I think some other logia's (theoretically) stack up
Aokoji v. Ace - Fire can beat ice, Aokoji is a good fighter so it would take some time, I just doubt Aokoji could face off successfully against that DaiEnkai Fireball Sun Blast
Aokoji v. Akainu - I would say ice would win, because this just has to do with elemental properties again, whilst Aokoji would be at a disadvantage against PURE FIRE, which cannot be frozen or cooled period, MAGMA on the other hand, can be cooled and pretty quickly, Akainu would end up having to "Rock Out" if you get what I'm sayin