Mitch, the default settings in the importer should at the most, be kind to your isp (as well as your browser if using IE), you can increase and decrease the speed in the importer file itself (threads per refresh i believe it is).
It may be a good idea to tell your hosting company ahead of time that you're planning an import to a faster and more optimized version of the UBB, I'm sure they'll understand...
But then again, it is usually easier to ask forgiveness than to ask permission...