These are the features I want to use from Speedbooster:
Remove query strings
Lazy load images to improve speed
Removes extra Font Awesome styles
Remove RSD Link
Remove WordPress Shortlink
Remove Adjacent Posts Links
Remove Windows Manifest
Remove the WordPress Version
Remove all rss feed links
Unless I am missing something, WPFC does not offer any of those. Furthermore, whether a feature exists in WPFC or not doesn't necessarily mean a user will prefer it for various reasons. If there is no actual conflict (my original question), shouldn't both plugins be allowed to be used. Maybe a waing that certain features can conflict would be useful (perhaps with a link to a FAQ entry explaining the potential conflicts) but not one that says the plugin needs to be deactivated.
Also, I am investigating Autoptimize but I didn't notice any waing for using that. Wouldn't that also present a possible conflict if you use all the WPFC features?