There is a pretty big difference between the 12' and 14' Glides.. Actually they're like chalk and cheese..

IMO the 12' Glide is a flat water 'do it all' sort of board that can be surfed and also do down-winders pretty well.. up to a point.
It's when the going gets rough that this board is not as good as the 14' Glide.. I think it's the sharp rails towards the front that cause it to trip or catch when the board gets hit with side chop and pushed sidways.. It's a bit like catching an edge snowboarding.. You fall and think what just happened.
Also in the open ocean you get bigger gaps between the swells and all sorts of lumps and bumps on the swells.. This is where the longer boards excell and the shorter boards become hard work.. The 14'er with its higher and thicker nose helps heaps in these rough conditions because pearling happens alot.
The 12' Glide has the advantage of being lighter and more monoverable and also easier to lift on and off the car roof.. It's also very stable and fast on flat water.
You need to demo both., Here's a link to what dogman was refering to..
www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=55297DJ