@Paul, aren't there other things that can (should) be cleaned up to increase speed?
... unused masters, ... ?
@ Kadrian,
How complex are your shapes. Is there a lot of background "shapesheet smartness" involved. Could simpler shapes decrease the amount of calculations involved?
An additional thought: waiting times are often caused by background routines trying to achieve something without success. Can you check your drawings on a other system?
What version do you run anyway? Could you try saving the drawing as older version drawing, re-load and test?
Just some thoughts. Paul is the forum's master of debugging.