Right now I am using a 7' medium moderate action Carrot stix for crankbaits that are 4' - 14'.

Should I get a longer crankbait rod for the 14' crankbaits? so the bait stays in the strike zone longer or will the 7' do the job just fine with some line conditioner that will add a little more distance to my cast?

Thanks.

If you have the room (storage and casting), get the longest dang rod you can find. 

A 7 ft. crankbait rod should do the job for up to 14 ft. If you are throwing DD22's or deep running Fat Free Shats, DT 16's, etc., a 7'6" or more will help you get them to the depth they need top be. I wouldn't recommend a rod over 7' for shallow running crankbaits. Those baits are more target oriented around cover with shorter casts and you need to have accuracy. Short little accurate casts for shallow cranks can be tough with a longer rod.