I can't see anywhere in the API where the feature statistics are available. I can't even see a good way to determine how long any given feature takes to rebuild. I did a quick modification to the "feature tree rollback animation" macro to see if I could check the amount of time required to roll each feature forward. However, the times I got didn't correlate to the feature statistics reported by SW.
That being said, it would be possible to iterate through all currently open documents, force a rebuild, and report the rebuild times per document (including parts and subassemblies). You would not have to open each document in its own window, just the top level assembly (non-lightweight) you're interested in. When you open an assembly in non-lightweight mode, all referenced parts are opened automatically in the background.
This macro would take some time to run, but it would tell you which of your parts/subassemblies were taking longest to rebuild. You could then narrow the field of which files to manually run feature statistics on.