If you are not using decimal, but binary/hex then it may be faster, with the new ANDB/ORB/XORB functions.
ANDB 255 will directly get last 8 bits,
DIV 255 then ANDB 255 will get 2nd 8 bits
DIV 65535 then ANDB 255 will get 3rd 8 bits.
...
Internally, each VAR has its associated timer value. RAM does not have timer value. To get to those bytes, we will need to introduce four additional variable names for each RAM, so that it will introduce 32 additional variables. Then internally declear internal variables and copy contents for operation. That is probably not much faster than above ANDB 255 method.
In few versions back, we added UROM1...4 read only variable, that is only settable through web GUI. Have you tried to use those to reduce some of your desireable value calculation? We did not make them to be PLC settable, because the EEPROM chip spec has very limited write cycles - easily worn out within a day, if there was a mistake in the PLC code. Those could be helpful, if you have a system need to be fine tuned during setup.