The Purge - Clearing out old iterations and releasing my frustrations

I decided to tackle a large purge job on a single product area. It was way to large to purge in a single shot. The goal was to keep only 2 iterations of Released objects. I estimated there were 120K purgable iterations in just this area. I will paste some graphs and notes at the end but here is what I learned:

• If too large, try determining a threshold by adjusting the number of iterations to keep and slowly walk that down.
• Purge Parts and CAD docs together. Too many dependencies to leave out one or the other.
• Use preview - HTML to get a count of the total number of objects found. I did not want to exceed 11000 items in a single job.  There is a preference to control this. 
• Chunk - There is a preference that controls how system chunks purge jobs. So a 10000 object job chunked at 1000 objects will create 10 chunks. Chunks are random so if an item needed to purge first is an a later chunk, dependent objects will failed to purge. See here: CS206660 
• Chunk of -1 will be a complete set. By far the best option to ensure the maximum number of items are purged. I was seeing percent success from 50-80% of objects removed. Using chunk of 500 or 1000 is ok but percent purged dropped to 33%. Successive purges then dropped to around 5 or 6%. You can increase chunk to 3000 but this will increase time for purge to complete often with little increase in success percentages.
• Eventually I was dropping the number of iterations to keep by 1 but that soon exceeded my max purge job limit.  You may have to skip to a lower iteration number with chunking to get the number of objects lower, then you can return to the previous iteration with chunk of -1 to get the whole set. 
• Running off hours had better run times but you do not make best use of hours in a day. 

Here is the data: