-->I know that there is a few version for the RCM6750.
To the best of my knowledge there is new version of Rabbit 6000 chip on the RCM67XX modules. It seems like ,to decrease the backup battery current consumption from 120uA to 50uA they modified the processor design on the modules.
Other than this there are no changes on the modules.
If you are facing any timing issue, pls directly check with the digi.