Hi Wombat207,
I don’t have a “spectrum” because there it’s not possible to quantify exactly how long any mattress will last for a specific person or predict exactly when you will decide to replace it because it is no longer suitable or comfortable for you (because this is the only real measure of durability or the useful life of a mattress that really matters) because there are too many unknowns and variables involved that are unique to each person.
Having said that … if a mattress is well inside a suitable comfort/support range and isn’t close to the edge of being too soft when it is new (see post #2 here) and meets the minimum quality/durability specs that are suggested in the guidelines here for your weight range (which it does) then it would certainly be reasonable to expect a useful lifetime in the range of 7 - 10 years.
There is also much more detailed information about the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here.
NOTE ADDED JAN, 2016: They have now introduced their new simplified choice mattress which has replaced their previous models and have also become a member of this site.
Phoenix