I have a typical rails app with partials to load nav bars etc. My mini-profiler shows one of the partials taking way more time to render vs the rest. Can I use mini-profiler to dig into the rendering of these to see where the time being taken up?
Have you tried running a flamegraph (click the "more" button)
To do so add the "flamegraph" gem to your Gemfile.
Once you get that done you should be able to dig in quite deep see: