Fragment by expression

I have a 200 million, 50GB table that I would like to improve query performance on. I am evaluating using Fragmentation by Expression. 90% of the queries use a date column as part of the where clause. I was wondering if anyone has used only the month (12 fragments) for the fragmentation expression, and if there are problems or issues to be concerned about (present or future). If so, did query performance significantly improve? One month of data will be archived every 13 months. We use HP-UX 10.20, Informix 7.24, EMC Disk Array (241GB on 56 PV's). Current queries take up to 40 hours to process. The current configuration for this table is fragment by round robin, 7 fragments (dbspaces) striped on multiple disks. We plan to re-org the database where each dbspace will contain two 2GB chunks located on a single disk. TIA, Mark Baumgartner DBA Cardinal Health