The effects are only temporary. After your members post a little, they'll be quickly labeled as either "member" or "well-known". Sadly there is no way to avoid this temporary draw back.
This actually is how imports to most any community works..... The importer automatically assumes you're importing 1 site into an existing community and so, those members would technically be new members to the already established community (host community).
I followed Jake's suggestion. I ran the cron job; editing the log in date into batches of 6 months 0-6months, 6-12months, etc.. Each time it finished in about 3-5 seconds. Processed 1,5 million members. No worries.