In theory[*], 71.beta5 should be better than 7.0beta6. But since it's still beta (and beta in MT world means less than usually in ICT world) you never know if your particular unit will like it better or not. So before you upgrade your unit, do the following:
- create (binary) backup (/system backup save name=<backup name> dont-encrypt)
- create text export of configuration (/export file=<export name>)
- fetch both resulting files to management computer
- ideally get installation package for ROS 7.0beta6 for right architecture (probably it's arm, but check what your device says under architecture-name in /system resource print)
Several things can go wrong when upgrading between different beta versions. It can happen that after you upgrade ROS, device simply won't boot (actually it'll enter boot loop). The only way out is
netinstall in which case you'll need either backup or export (done in bullets #1 and #2). It can also happen that device will boot after upgrade but the configuration will be somehow damaged (the same could happen if you have to netinstall the unit and you'll use backup file to restore configuration). In this case it's best to reset unit to factory default configuration and apply minimum needed changes ... looking into textual export (done in bullet #2) will help you in this process.
If everything fails, you can still try to downgrade unit to current ROS version (hence bullet #4), in this case restoring from binary backup (bullet #1) should succeed.
[*]it's well known that in theory there is no difference between theory and practice, while in practice the difference is huge