Need Advice on Selecting Shingle longevity rating

I realize that the guarantees (30 year, 40, lifetime) are about 99 percent marketing hype, but my real question is "Does buying a lifetime versus a 30 year for example, really get you much more service out of the shingle, given an equally good installation job?"
In other words, are they both going to start looking pretty bad in 20-25 years, and need replaced?, or will the 40 year or lifetime grade be holding up pretty well after 30 years or so?
Appreciate any advice.

Johnny Boy,

I re-roofed my house last year and had the exact same question. After much research, I learned that many people on this site think a 30 year Certainteed landmark will last as long as a lifetime shingle, if installed properly. Seems like these lifetime (40,50 year) shingles have only been out a few years. How can we prove the longevity of them?

I did end up installing the Owens Corning Duration Lifetime shingle, but for the following reasons:

-Live on a lake, so I like the higher wind guaranty
-Better looking shingle, much bolder shadow line
-Much Thicker shingle - looks better! 4 bundles per sq as opposed to 3 bundles per sq.

I have been very happy with my shingle but I am sure I would have been pleased with the 30 yr landmarks. Just not as pleased:). I really do think my shingles look better, but I question the longevity over the landmarks

Good Luck!