The following command will show the cover flow frame rate (as frames per second) within the Finder alongside each filename when flipping through files.
defaults write com.apple.finder IKImageFlowShowFrameRate 1
To make the command take effect, you need to restart the Finder.
Revert to the default setting:
defaults delete com.apple.finder IKImageFlowShowFrameRate
You need to restart the Finder.