You can select Tools > Developer > Profile Plugins to get a profile report showing how much time plugins are taking to respond to events.
There is no “safe mode”, but you can simulate it by adding all of your user installed plugins to the ignored_packages setting in your user preferences. If you only (or even mostly only) have packages installed via Package Control, you can use Preferences > Package Settings > Package Control > Settings - User to open the Package Control settings file and copy the contents of installed_packagesto disable them all.
Additionally if you’re using Windows you can test with the portable version; that version ignores the settings in your user profile, which is a fast way to get at “baseline” reading.