Current recommended Snom firmware versions are:
6.5.20 (with linux 3.38 and jffs2 file system)
7.3.14 (with 1.1.3-s bootloader or higher)
7.3.29 (with 1.1.3-s bootloader or higher)
We do not suggest V8 for Snom3xx series phones unless you need OCS support or you are feeling brave.
7.3.29 seems to fix a few minor issues with long term stability. This is for users who take hundreds of calls per day and who use the DND feature. Has fixed a lot of people’s issues.
If you use Action URLs then please use 7.3.14 or 7.3.29. Otherwise you may have issues with call transfers.
Above my opinion based on supporting Snom phones in the UK.