I have both the Casio 310, 300 Yamaha P120 and the new P140 in my store.
Yes, the Casio 310 is a major improvement over the 300 for the exact same price ($599.00). The new Yamaha P140 is also miles above the Yamaha P120 in terms of piano realism and features and both are the same price ($1195.00). The Yamaha is 64 voice polyphony and the Casio is 32 note polyphony. If this is not a huge difference and price is, select the Casio. If sound quality and piano realism is most important, the new Yamaha P140.
George Kaye
Kaye's Music Scene
Reseda, California
818-881-5566