Been 400 for some time. It has not been worth it for expansion content. At 350, you unlock the +1 Tier upgrade and can (and should) do only the two Weekly Story missions on Mythic which guarantee a Tier 5 weapon that your vendor focus is set to (but only twice per character per week) The final 3 portal Conquests were however, and gave multiple Tier 5 weapons upon completing them. The Solstice Event gave out Tier 5 armor like candy and the 3 weapons are better than any of the Kepler weapons (which makes sense I guess) I don't understand why at 400 power, Kepler doesn't even have a small chance to reward you with the best it can offer in The Sieve activity which is timed.