As an update:

The importer ran for two full hours on 2,900 topics with 124,000 posts. Server load before starting was .5, load spiked up to 4.0 with it averaging around 2. This was done on a new server with no slowdowns of the other sites noted. I was working with the new server admin/owner and we both agreed that the old server might have died if I had tried the importer before moving.

I ran the test on:

http://www.haroldandrews.com/testforum/ubbthreads.php

to convert it to:

http://www.haroldandrews.com/importtest/ubbthreads.php?ubb=cfrm

I'll leave these up for a month or two before deleting along with my production 6.5.1 board.

Thanks again, Rick!