Sure, dealing with this in a less public way, we can move this to support@mcneel.com and work thru the issues.
I can take you through all the possible ways we test it. This just takes a lot of back and forth as we brake down were the slowdown could be.
You are correct, this is not uncommon. The problem is that there are many different things that can cause it.
A newer tools we are working on to find the issues quicker is this: Rhino WIP Feature: New Audit3dmFile…Graphically