Actually certainteed is one of the better manufactures to deal with when handling a warranty issue.We could start a great debate on this forum just having everyones opinion on 30yr manufactures and we would probably never even touch on the subject of a 40 or a 50.My opinion is this a 30yr is the way to go, reason being the roof logically will not make it past 15yrs.
It also depends on your climate, different climates require a different material, generally all shingle manufactures have websites and on those sites they have a diagram of the U.S and on the diagram it shows where each type of material to be used along with the climate of that region.The 40's are thicker than the 30 and the 50 is thicker than 40, and the 100yr is thicker than all three.The price difference between a 30-40 isn't that much.,My opinion is a 30yr timberline has a better performance and weight factor than Tamko, I feel that the O.C durations are a great product and if you are feeling froggy O.C duration premiums (lifetime) have a nice earth tones. The thinner the shingle the less material to manufacture,the thicker then you know where its going.To give you the most honest answer will be acknowledged. A standard 30yr sq. consists of 3 bundles the 40yr shingle requirer 4 bundles per sg,and the 50's are also 4 per sq but they are thicker bundles.And the 100yr shingles are 5-bundles per square.So that explanation proves that yes the difference not only on the wrapper as being a 30,40,50 or 100 tr shingle but is validated by the fact that more bundles per square equals more materials being used to manufacture. Hope this helped.