Suggestion: New Testament Text and Translation Commentary by Philip W. Comfort

This is a great resource for working through many of the textual variants of the New Testament. It is much more comprehensive than Metzger's and it interacts with many of the modern translations (and which variants they base their translations off of). 

I would love to see this resource in Logos. I would even be glad to be contracted by Logos to digitize it if needed [:D]