Yamaha PSR-E423 or PSR-550

[paisleypark]

Hi,

I am looking to buy a new keyboard and at our store we have the following: Yamaha PSR-E423 or PSR-550 (double the price of the E423).

This will be my first keyboard. I am a piano/keyboard newbie. However, I am after the clarity of the sound.

What is the main difference between the 2 items?
Which one will sound better?

Is the 550 that much better to warrant the double price tag?

any advice is very welcome.

thank you