How can I find out whether by emacs was built for 64 bit, and/or wide-int?
https://www.emacswiki.org/emacs/EmacsFileSizeLimit
Old versions (i.e., anything before 19.29) of GNU Emacs had problems editing files larger than 8 megabytes. This limit was pushed further, first to 128MB (since 19.29), then 256MB, and 512MB (since 23.2). On a 64bit system, the limit is much higher than anything you might reasonably be able to open for the foreseeable future.
@lucifargundam hmmm... I'm really not catching any leads there