I have read that I can do this to make a smaller footprint Nginx when used as static content cache/reverse proxy:
--without-mail_pop3_module --without-mail_imap_module --without-mail_smtp_module
What other options are safe to disable? SSI, FastCGI? Others? The only requirements for the reverse proxy is to be able to do https and gzip compression. Will disabling all the module really help with footprint and/or performance?
Nginx is pretty fast by default, smaller footprint will only help if you are really trying to work with a memory starved system like embedded systems or something. Disabling the mail modules can help a little but I would not advise to disable the http related stuff (even if you don't think you won't need it, you may end needing it someday).
Binary size really doesn't has anything to do with performance, since stuff is all addressed by memory address on RAM (it's not like the kernel will take more time to run a function because it is "further" from the "binary begin").
The documentation has some info on what you get when you disable SSL, rewrite and pcre stuff, and this site has a nice writeup of what modules are needed for what (modules in Nginx are added at compile time, not as shared libs like Apache).