How much difference would a new (wave) fin make over an old scratched up one thats got next to no flex in it?

Want to get an idea for the difference it might make before making a purchase...

cheers,
Ben

I'd second that - the fin is one of the most important parts of the whole setup, and once you've used a good one...

I am i to late to fourth that .it always sames that mr. blue juice is always one step ahead of me when looking for a new fin you must take into conisderation alot things .stiffness ,tip flex , size ,foil shape and what you will be using it for waves, salom,formula and freestyle in the old days one fin did every thing now days you need at least 2 fins for every board you own which makes for lot of fins and they all work different so you must decide on e.g 85l wave board , 5.7 wave sail and you weigh 80 kg 15 - 18 knt sea breeze . you will proberly go for around 23 medium in this lite wind you will want to load the fin to get the board to plan . a to stiff fin will cause spin out as well as a to soft, in these conditions but every thing changes again as the wind increases or drops out . this is only one story in the big world of finage