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, 23 Master Series.
Nadal 14 GS, 27 Master Series, 1 Olympic Gold.
Djokovic 7 GS, 4 Year End Masters, 20 Master Series.