Don't want to seem like a cynic against Pentair at all here, but their logic seemed flawed to me. I may be no expert on SWCGs, but, from all the experts posts here, the biggest reason for a failure is not saltwater. A properly maintained chemistry in the pool water and any cell should last at least as many hours as advertised. After all, it is a SALT water chlorine generator, what other kind of water would be in the pool?
I have about a 12,000 gallon pool. The PB listed a IC20 for my build, which is just under the 2X recommended level. I ended up going with the IC40, thinking I would need to run it a lot less and it would last a lot longer. The difference at the time was like $200, so it made sense to me. PolyTech Pool lists the difference of the IC40 to the IC60 as about $300 right now, which doesn't seem all that bad considering how much less you would need to run it and in theory how much longer it should last. With a low RPM and running the pump 24/7, and a auto cover, I run my cell at 15-25%, depending on the amount of sun and swimmers at any time in the height of summer.
I think with a properly balanced pool, any cell should last as long as the advertised hours, so why not get the bigger cell? The question would be the conviction this issue will not happen again and maybe you just got a bad unit. But going with a vendor who will get you the full warranty sounds like a great idea.