I think it should also be mentioned that the Purr Data GUI is more CPU intensive than Vanilla. It probably doesn't matter much on faster machines, but it might be a factor if you're running on a slower machine.
That's true-- you'll definitely notice the difference on a machine with single CPU. On multi-core machines the GUI shouldn't be getting in the way in the course of normal patching operations. (Especially if you run Pd with realtime priorities.)
The actual chatter between the GUI and audio process should be less, though. For example, if you move a selection of objects it's just a single message rather than one message per object. Also, textbox edition doesn't touch the audio process until you re-instantiate the object/message.
But like Pd Vanilla, you can still trigger dropouts by moving the mouse over a patch if there are enough objects on the canvas. Someone started doing work in the direction of fixing that. But it's very tricky to get right without breaking some random Pd ninja's use of Pd's unspecified interface.
However, you can set event callbacks for the new
[draw] commands without sending streams of "motion" messages to the canvas. So there's that.