What size batches? The advantage to running two 240v 4500w elements vs., say one 5500w element is that you will reach mash and boil temperatures faster. The disadvantages are that you will need to size everything to account for that amperage draw. Frankly, unless you are talking really big batches, using 30 gallon kettles or larger, I don't see it being worth it.
Much more valuable, IMO, would be having a pump so that you can recirculate and maintain tight mash temperatures. Otherwise, you will have to stir frequently.
Regarding the PID, it will certainly work, but it comes with a K type thermocouple. A PT100 RTD sensor is more accurate and less fussy.