Larger ROM does not translate to better voices. a 64mb sound set can sound better than a 175mb sound set. It's all in the quality of the raw waveforms themselves.
The S-700 is going to give you Mega Voices.. That alone is a biggie. Those Mega Voices will make some styles stand out more on the S-700, plus they're just darn fun to play with too.
_________________________
GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.