I think a choice between the 100-500L that you already have and another $2K for this is kind of a slam-dunk non-choice. The real market is guys like me who can't spring for the L glass, but would like to have a decent telephoto. For a consumer model, the RF100-400 is a fantastic lens, and I don't regret a single penny of the $650 I paid for it. If this lens is anywhere near that IQ, it's going to be a popular one. $2,000 is a little bit beyond my normal means, but it gives me a lot to think about. I have the RF600, which I just am not happy with for a few reasons. (One being that in practical use, I realize that I should've purchased the 800.) I've been considering selling the 600 and getting the 800. Now I will be thinking about scraping some extra pennies together to get this lens instead. Especially if the IQ makes this a good compliment to the 100-400.