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The larger Surly is about 3 inches wider and the adjustable hardware is going to weigh a fair bit compared with the HC with it's fairly set mounting points.
Still 500g lighter than the Soma, VO or the Nice Rack, combined it with a Tara and it weighs the same as the above but you have a lower mounting point for the panniers than the first two which should help in most scenarios...
STW have more photos of both mounted to bikes http://singletrackworld.com/2015/10/new-surly-front-racks-launched/
860g! that's pretty high.
My Haulin' Colin Porteur rack is around 400g for a similar footprint.