Buying a new board

[surferog]

I have found what i think is a bit of a bargain - second hand fish - 150 , but before i part with my cash, i just want some advice from you lot. I am currently riding a 6'2 x 18.5 x 2 - the coke board from my pic. I am 5'10, 11.5 stone and a fairly decent surfer, but i am growing fed up with surfing underwater to be honest, so i have found this fish 6'6 x 20.5 x 2.5, with a quad fin set up, and option for a fifth. I would be using this for the rest of the summer, possibly into the winter. What do you guys think - to big, to wide?????? What would you advice me to look for?