Just wanted to know for my XC build project.
I'm sorry but if your really bothered about the weight difference between these two "non top of the range" disc brakes sets then your barking up the wrong tree. There are far far lighter brake sets about but they will cost you a lot more but that's part of their selling point. The two you've mentioned are just good medium priced sets so if your looking for a decent weight saving then try your tyres or some other parts because these aren't part of that group. That said you'll be happy with either set ok.
I know what you are saying, and yes you're right, but I actually have a full set of Juicy 5's spare and some SLX brakes on a mid priced XC bike I am getting. I would leave the SLX brake set on the new bike, to save the hassle of re-cutting brake pipes etc, however if the Juicy 5's come out much lighter then I would swap them over.
tried google, weight weenies?
Can't imagine there'd be a huge difference in weight.