There is no real distinction between WinCE 5 or 6..all versions of Igo/Primo should work the same.
Any of the "2.4" variants (versions 9.6.xxxxxxx) should work. Differences between one 9.6.x release and another are minimal or non-existent...some minor cosmetic changes or nothing noticeable at all with no changes in function either. The most important factor is to find one appropriate for the resolution of your device.
"9.8.xxx" is up and coming, but so far it is troublesome for many.