I need to create a template that will validate the values entered against
external spreadsheets upon saving. Before I begin, I want to make sure I use
the best method for returning the values quickly, as some of the templates
will be completed with 16000+ rows, and each row would have to have 4
validations to the external files.

The previous version of this template opens the external files during
execution, but this process can take up to 20 minutes. I am currently
thinking of adding links to the file with vlookup functions rather than
actually opening the file, but am wondering if that will be slow as well.
Any ideas to make it faster?