@JaneCavanaugh we have done a couple conversion from Providex to SQL. They went FAIRLY smoothly. We did have one issue where a registration or system file was created that prevented us from reprocessing the conversion. The issue was discussed here on socialcast and the solution was provided. You can search for the entry to get more info.
As you pointed out, the legacy (non-new framework) modules do not move forward. Neither does Business Insights Reporter. I'm sure there are other gotcha's lurking but so far, nothing significant.
Speed has not been an issue for those we have converted (whew!) and reporting is much quicker.
Don't forget to grant you end users rights in SQL to at least be db_readers if you want them to have access to the data through outside programs like BizInsights, RenovoFYI, Excel, Access, etc.