Thanks for the reply, Graham. Using an APS-C camera I'd like to shoot as wide as 18mm (28mm eq. in FF). As I've been researching I keep coming across the 720nm / 680nm thing; still getting my head 'round it. I'll be using Formatt 85mm filters and their aluminum holder with the 95mm circular front attachment so I'm limited to 95mm hot mirror / IR cut filter sizes for the sake of affordability. Going by your experience with the B&W it looks like my only affordable option is a filter by a company I've never heard of, Cavision.
Lots to learn, still, so thanks for the insight.