The Corsair HX 850 is only partially modular, so some of the cables are hardwired. If you get to the point where it matters how everything looks inside the rig, you´d want a tidy cablel arrangement. Having a fully modular psu means you decide exactly how many wires you want coming out of the psu, no unneeded wires to clutter up the case. And you can also get these slick coloured single sleeved cables, that you could then replace the stok (black) cables with. HX850 is gold certified, so efficiency is good.
For a fully modular psu I could recommend AX 860, platinum certified, that means even less electric energy lost to heat.