I don’t think you will have issues in the upgrading, in a basic configuration, and on a device without wi-fi the changes (if any) should be minimal.
Take into account that 7 is a bit slower, some say by 15%, some say by 20%, some say …
so, if your old Hex performance was fine with v6, you won’t notice a difference with 7, if it was on the brim of collapsing under the load/speed/bandwidth/whatever then maybe it is better to leave it alone on v6.
Now the good question:
At which exact version of 7 do you plan to upgrade it? 
Remember Rule #10:
http://forum.mikrotik.com/t/the-twelve-rules-of-mikrotik-club/182164/1