I'd say Symbian^3 is of the same generation as a patched Maemo 5, not Maemo 6. Symbian^4 is the future contestant to Maemo 6. If the rumored S^3-equipped N87 12MP comes true, then the S^3 platform can be considered as a half step toward "the big one", or Maemo 5.5 equivalent if you prefer.