In my case, our group of players realised that you can do incredibly broken things with Mythic, and we have a 'Gentleman's Agreement' with our GM (this was his idea). We don't super optimize, and neither will he.
We have 4 players (2 vets, 2 intermediate players), traditional class roles and a 15 point buy. Wizard (Abjurer), Cleric of Torag (Good/Glory), TWF Rogue and a Paladin. (Okay Oracle/Divine Scion/Paladin, but that's the exception.)
There have been a few fights where we dominated the field, but not too much more than any other AP. The fights have been quite challenging, but as I understand it our GM upped the CR's because he agreed that 1 tier does not equal 1/2 CR. The Wizard is starting to pull away around Book 4, though. As the Rogue I just can't keep up with the things he can do. Again, that happens in normal games though...