I never used the Hair Room in P6 cause it was just too slow. Yesterday I tried it in P7 and had 16,000+ hairs in Show Populated mode and could still move the head around easily.
 
Haven't had a crash, lockup or other problem of note with two minor exceptions:

Once the ENTER key would no longer start and stop playback of a 450 frame animation and 

on frame 1 of the animation, an item I had keyframed invisible, would not toggle back to visible with the mouse, but Undo worked. I see there is also a Visibility Parameter Dial, so I could have probably used that as well.

I set my Undo's to 32 because I can't see ever needing more than that before I've saved my work anyway.

 
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