I think both are attractive, for different reasons. The 407K has a larger dot, which I think is an advantage over the 2 moa dot on the 507K, but the 5 series has the circle dot option which the 4 series does not. As much as I think the circle dot is a disadvantage for pure technical shooting, I think a circle dot is a great carry reticle because it isn’t subject to multiple dots in weird light, and you may find the circle dit more reliably with a poor index.