For Ret? There's only one relevant breakpoint, at 50% unbuffed melee haste. That's the point where the GCD caps at 1 second. The only spells that have breakpoints are Censure and Sacred Shield, which don't matter.
There is, actually, a theoretical breakpoint at roughly 40% haste where mastery jumps in value on any fight with 4+ targets. But that's largely immaterial unless all the boss fights in SoO are consistently 4+ targets, otherwise haste should continue to stay superior up to - and probably past - 50%.