I've been shooting Production for several years and have a mount and red dot ordered to shoot my Sub2k in PCC. I can't wait until it out runs all those JP carbines for about a third of the cost.
It comes down to the shooter. I can pull triggers pretty quickly and keep up with my friends who have JP. Does that make the S2K better? Depends on what criteria and who is shooting it.
It is like a Porsche vs a tricked out Honda. It is possible for a Honda to beat a Porsche but it is still a Honda.
Anyway there have not been many rules regarding magazines. I don't think you will be faster with a weapon mounted mag unless you are used to reloading from that position all the time and can do so fast.
The benefit to PCC is also there shouldn't be a need to reload if you are in a free state. I run 35rds in my extended mag, that gets be thru all the stages without reloading.