Starting with the Slice Intelligence data, orders for the first one hour of U.S. pre-orders on April 10 was 800,000 Watches of all varieties. 600,000 Watches were ordered the remainder of April 10 for a total of 1.4 million Watches on Day1. Only 550,000 watches were ordered from April 11 through April 26!
The questions that need to be addressed are 1) whether Apple will continue to ship Watches at the same rate or will they drop back to a slower production rate (were Quanta and the other suppliers working overtime to catch-up with the backlog) and 2) when will Apple begin to divert Space Gray Sport Watches to their retail store.
Using a combination of Slice Intelligence data and my own conservative estimates for the period beyond May 18, approximately 840,000 Watches were ordered in the U.S. from April 27 through May 27.
Assuming 260,000 of unfulfilled orders from April 10 plus the 550,000 for April 11 - 26 plus the 840,000 for April 27 - May 27, the backlog as of this evening is 1,650,000. This causes me to reason that Apple will continue high levels of Watch production and will likely delay diverting Space Gray Watches to the retail stores until the backlog of unfulfilled Watch orders is much lower.
All this to conclude that I estimate that you will receive your SGS Watch no later than June 9.