NOP
If you do something like
CPT C "A + B"
or
Add A B C
Then the add is definitely going to be much faster.
If however you are doing something like
CPT C "((A+((B-A)/Rate * (Timer1.Acc/1000.0)) + Offset)*)16384"
then the CPT instruction begins to be an advantage. There would be six intermediate results and storage operations in ladder.
As I indicated earlier, I have not tested it myself, but I was told by one of Rockwell's own that ST was faster than ladder for math intensive routines. I know that a lot of maintenance guys dont like ST, but then in my experience, most of the time the maintenance staff is looking for a limit switch that is not being made or some such malfunction and rarely concern themselves with any actual calculations.
I am the guy that gets called at 3:00 in the morning, so I usually try and write my code to be as readable as it needs to be. I even talked about some of my techniques in another thread, but there are certain routines that once debugged can be thought of as black boxes - the code is predictable and sometimes its the kind of thing I don't want a maintenance tech messing with. I recently had to put a password on a PLC (something I hated doing as I despise the "kingdom builder" mentality) because one of the techs just wouldn't leave it alone. We just couldn't convice him that the sensor needed frequent calibration instead of tweaking the numbers in the PLC just to get it to run marginally. Since locking it down it hasn't given a single problem as he is now forced to do keep the sensor calibrated. If I would have had ST available on that PLC I would have used it rather than lock down the PLC.