Well done on the ID! I agree. Xiphydria looks right. I think I'm long overdue for buying a guide. You seem very good at IDing.... what would you recommend?

As far as guides go, I'm at a dearth of book resources. For insects of NA, I have several old, simple field guides: the two National Audubon Society guides here and here and a Pocket Guide. However, I use these strictly for general referencing, such as looking up information for insect families. I rely heavily on memory when making an ID. Having spent much time over the past ten years (pretty much half my life) burying my face in field guides as well as countless image-laden library books, I'm familiar with the "shapes" of many insect families, and often recognise many by their common names. However, to go into such details as scientific names, I'm forced to resort to updated sources such as BugGuide. All in all, knowledge of guides and accumulative experience turn out to be most helpful when making your own ID's. It's a continual learning process that is not always easy - often, it's safest to consult the expertise of specialists. I do that often at BugGuide, especially when I have a hint of doubt over my own identification of a particular subject.
A "real" guide that I recently bought is the Kaufman Focus Guide for Butterflies of North America. As for recommendations, guides like this and this might be good for starters. Hope that helps!

Xiphydria maculata