Use longer warranty shingles?

[Sol Bergren]

I'm having new shingles put on a duplex and the roofer has two options:

1) BP Mystique 42 Limited Lifetime Warranty Shingles  (base shingles)

2) Malarkey Vista 40 yr Warrant Shingles (+$950 upgrade)

Roofer figures upgrading from base shingles will extend shingle life from about 20/25 to 35/40 years.  I'm leaning towards using the upgraded shingles but curious to hear others thoughts, thanks!