I copied an install of SR7 over from my netbook and updated it to 4.0aB1. I hadn't yet reindexed the netbook. So, before going to bed I decided to merge the indexes.
I couldn't believe the short guesstimate that was given, so I watched the index log. The process now does merge the supplemental and main indexes.
My main index and supplemental index for a library of 3822 indexable resources was rebuilt in 59 minutes (the merging took 48 minutes).
I am so impressed.....