Re: Has David Ferrer reached his ceiling?
Yes, unless he improves his serve.
Federer certainly, and to a lesser extent Djokovic and Murray all serve distinctly better.
The current greatness league of active players in order of achievements to date (a factual comparison rather than fan biased assessment):
Federer 17 GS, 6 Year End Masters, 21 Master Series.
Nadal 11 GS, 0 Year End Masters, 24 Master Series, 1 Olympic Gold.
Djokovic 6 GS, 2 Year End Masters, 14 Master Series.