Hi Zuni,
Higher density foams are more durable than lower density foams (although there wouldn’t be alot of difference between 3.7 lb and 4.1 lb in terms of durability) but there are also other factors involved in the useful life of a mattress that you can read about in post #4 here.
These are two very different mattresses and because they are so different I think that the suitability of each one for your body type, sleeping style, and preferences would be an even more important consideration. Regardless of the useful life of a mattress or its relative quality/value (and all the mattresses made by the same manufacturer would have similar “value” across their range) … a mattress would have little value to you if it wasn’t a suitable choice in terms of PPP (Posture and alignment, Pressure relief, and personal preferences). Outside of personal testing on the same or an equivalent mattress … the most effective way to choose a mattress would be a more detailed conversation with the retailer or manufacturer who sells it (see mattress firmness/comfort levels in post #2 here).
Phoenix