Movement Speed has a total Cap of +100%, +50% cap for MS affixes. Movement Speed from other sources could be used to get to +100% without using affixes, and Epiphany affects the cap of MS affixes only.
you could have +62.5% Movement Speed affixes on your Equipment and another +50% from other sources.
found this with a Search 
, hope it helps.
if you have the Direct Boost mentioned in the Post, but no Skills to get the other +50%, you could use Draught Mythic instead (I did this with a Momentum build a long time ago. I usually used Draught when going against Epic+ monsters or tough mobs). it replaces your Potion button but you get the +50% Movement Speed and +50% to APS. Draught has a 5 second cool down and lasts for 5 seconds (as of Patch 3.0).