All I want to do is slide everything from now till end over by some amount (e.g. quarter note). I can't use nudge because it has a bug wherein notes to the left of now get deleted, so I try shift-drag. X2 hangs for about 15 minutes before it finishes.

Preferences > Customization > Editing

Switch from Slide Over to Make Room to Blend Old with New. The "Make Room" setting has never worked properly in the Track View, and I believe it might be implicated in this PRV issue, too.

In addition to this, if you have to move a lot of notes, it's best to split the clip and slide, nudge or drag the clip. Moving large numbers of notes within a clip has always been problematic. You can bounce to clips later to recombine them. 

I could be completely wrong about this but I thought I saw a similar post to this and the solution to dragging large number of midi notes is to first turn of the feature that plays back midi notes when selecting. Sry, not sure what feature is called or where it's located. 

I could be wrong, too, but I don't think the audition settings make a difference; they're in Preferences under Customization > Editing now.