In summary, it won't be a simple fix but I think if you cover the three major bases you can get the performance of these reports greatly improved:

1. Ensure your databases are optimized and indexed regularly - fix those fragmented indexes.  This will cut down the time it takes for Crystal to get the data to collate.
2. Switch to Datapipe instead of ODBC reports where possible - this will greatly reduce the data sorting and collation time once Crystal receives the data.
3. Avoid redirected and follow-me print drivers from generating the print previews - especially for reports with hundreds of pages as the text might be flowing to the driver as hundreds of pages of bitmapped graphic instead of text, even though its just text.  This will cut down on the preview generation time once Crystal has collated and sorted the data.

Good luck!

After trying several things, in the end the fix was a DB Dump/Load. 

After trying several things, in the end the fix was a DB Dump/Load. 

Hi DeniseB this makes sense, doing a dump/load will fix MANY indexing and performance issues without having to do any maintenance on the data.  Its always temping to migrate data to a new server doing SQL BAK and load to save time, but unfortunately it breaks all the indexes and leaves the data in a poorly performing state.  You won't notice this with small data sets so this must be a decent sized database!  Great work!