A good philosophical question, for sure. Really would depend on your subjects more than just a "yes or no" answer, or at least that's what I'd think. Lenses can only go so fast due to limits of physics and design (and COST!), but it looks like ISO can be pushed up incredibly. Everything comes into play with this question, and I certainly have no answer. I rarely ever shoot any faster than 1600, and that's a rarity itself. With so much available in PP, does one really need extreme ISO or expensive ultra-fast lenses? I would guess for fast moving subjects only, and if you aren't shooting sports, what would be the need to go radically higher in ISO over having faster lenses? Comments, anyone? Just to satisfy my own curiosity!