1. Currently I have my GMC Sierra 1500 rcsb cammed lq9 idling stable at 725 rpms once up to operating temp.

I was wondering if there are any benefits to have a STABLE, lower idle rpm than that. Something like 600-650rpms.
Would there be any noticeable mpg increase, or anything else worth note?

2. My injectors are supposed to be 8.1 marine injectors, am I right by having my flat vacuum referenced IFR table at 43.8?