Put that RB on a Op/Tech and watch it SLIDE right off your shoulder.
We use Up-Straps on EVERYTHING, I use one to carry a Canon 1V-HS with a 200mm F1.8L lens and a complete Mamiya Universal fully loaded and it WILL NOT slide off your shoulder nor will the strap break.
They have 2 models one with kevlar in the strapping. Neoprene is for women !!
You can order the strap lugs from Op/Tech and then use them on your Up-Strap !!
Let me know if you need some more information.