When I ordered my SR/S I had a top rack (Zero part 10-08280) fitted by EEMC. I didn't go for the Shad hard luggage as I intended to go the soft luggage route. Knowing that aerodynamics can make a difference to energy consumption, a soft tail pack should be better suited to extending touring range than a hard top box. (I haven't done the back to back testing, so it may be that the aero difference is so small that the additional security and convenience of a top box is worth the energy consumption penalty. If someone has done that testing, let me know where I can read about it.)
But I've chosen to go with soft luggage, so having a top rack is key. The Zero rack is trapezoid shaped, following the lines of the bike's tapered tailpiece. It's made from 1.5mm thick powder coated steel, lasercut with slots for lashing, with four standoffs welded to the underside and is rated for carrying just 4kg of luggage.
After a couple of months' of use my two main observations are a) the lashing slots aren't well positioned, and b) the tapered shape doesn't support rectangular soft luggage. The former is more of an issue than the latter.
As you can see from this photo, ideally the lashing slots at the corners would be aligned either transversely or longitudinally, rather than on the diagonal. And the rearmost slots are almost entirely useless at that angle. The solution here is to buy the Ducato Panigale 899/1199 web loops from Kriega, and bolt these to the Zero top rack.
With some M6x20mm bolts with flanged heads, 20mm diameter penny washers, and flanged nylock nuts, you can bolt a web loop to each corner of the Zero top rack.
That works pretty well, and the nylock nuts mean you don't have to fully tighten the bolts, which means the web loops can still rotate for optimal lashing, and you won't lose the nuts due to road vibration. And the aesthetics are far better in my opinion than my original attempt at the top. The downside is that the bolt heads stand proud of the top rack, which could damage the underside of your US-Drypacks if they're not lashed down sufficiently and move about during your ride.