Nice selection. 200 Points dead even and the option to take them as troops OR fast attack depending on whether or not you deep strike them. Very versatile - I like that.
The only downside is that someone only needs to pop 3 of your Grey Knights for you to lose. Now they do have power armor so they get a good save throw, but take a look at the following...
As an example, if you go up against someone decked out on say 12 Space Marine Scouts with bolters, and one with a heavy bolter you may have some problems. That's 199 points and potentially 27 shots per turn coming your way if they rapid fire. That's statistically about 7 wounds and after save throws you'll probably lose 2 per turn, leaving you thin for victory conditions. Now yes, you do have your special abilities like FNP, etc. and your psycannons will eat through their armor as if it were not there, but you've got to take out 6 of his guys to achieve victory.
I still like your list, but small points games can be tricky sometimes in getting the right balance of numbers to strength of warriors. With Grey Knights, you either build it exactly like you have it, or replace your psycannons with more knights for increased survivability. I don't really see any other way to field them.
I'm just playing Devil's Advocate here. Of course as always, it all comes down to die rolls!