Best option is what you mentioned already which is the 2-part combo to Purge some IM5 records first then to reclaim the actual space still occupied by the purged records, choose Optimize in Rebuild Key Files. 2nd option involves getting one of the MD types (.. ahem ..) to change the start up code of 4.30 to support segmented files then at the point it will create the .001 file and then later the .002, etc. Later if you upgrade them to say v2018, the I/M Conversion program will know how to read the 4.30 segmented files because (since 4.40) it already has the hooks to support it.