Well it's just simply physics, a longer, wider board is going to be more stable...BUT...if/when you want to go out in big wind and go faster, and jump waves, and do duck-gybes, and barrel rolls, etc. you need a short board to do that.

A long board is great for learning, but just like racing cats, as soon as you 'master' the one you have, you want to get something faster!

I'm sure this will be you, by this time next summer Pete, jumping those huge waves just off Marco Island! ;^)

http://www.youtube.com/watch?v=kfN3WwI6qAM

I just hope this guy is NOT your instructor! http://www.youtube.com/watch?v=zEXMaOOJQck&feature=related