Congrats - I would love to get this card one day.
On the reduction of your initial granted SL, you are the best to know your comfort level of course.
WIth that said, given the number of your cards, there maybe another approach on keeping your overall exposure under your specified dollar amount.
For instance, you have both the Amazon Prime Visa ($3,000) and the Amazon Prime Store card ($1,000). While the former is Chase and the later is back by Synchrony, these two cards offer basically the same 5% on Amazon spend. If you were to close one of these, say the Store card, then you would be able gain this $1,000 back onto your new DU. Just my thoughts.