As long as you are looking at your critical rating, not your total critical chance (which includes what you get from aim). When people talk about diminishing returns on crit they are talking about the crit rating stat specifically. The common mistake is that people refer to the crit chance number on the character sheet as the benchmark for diminishing returns.
In best in slot 27 mods crit rating sits at around 265 for pyro powertechs if your using the battlemaster pvp set bonus. Its important to keep in mind though that stat priorities change as your stat budget goes up. Lots of great info here: http://mmo-mechanics.com/swtor/forums/thread-446.html