XCAL II has a few more tables (timing vs heat, spark, correlated variables) in them that the Predator does not. If you are a dyno shop working with S/C's and NOS kits, and pulling max power out of highly tuned vehicles, yes, most of the shops use SCT.
For the average guy in the street, Predator works fine. I have as about as good as a tune as I can get from my mods at around 315 rwhp with Predator, going to a XCAL II wouldn't get me anything more. However, if I S/C, then surely, I would go with a XCAL II to keep everything safer.
My dyno shop had a 2004 Cobra with a Predator tune making mad HP, he burnt a piston after the engine got way too hot dragging mid summer, he had the motor rebuilt and was adding a KB blower when I saw it last and going with an XCAL II tune and dyno.
It will be a fuggin beast.