there is quite a bit of difference between the 70's and the 60's rods. yes, they are 70,000 psi, 60,000 psi rods.
grinding down 6011 rods are like cutting through rebar, 70 rods leave a much harder metal behind.
7014's give you a weld that looks close to a 6013, with a bit of undercutting at the edge of the bead, but with much more penetration.
I use 7018's because that's what I can buy locally, but I don't like the slag it leaves and the weld doesn't look as nice.. but that might just be my welder.
6010's i've never used, i'd imagine they are just like 6011's which are great for welding rusted rebar together and that's about it. they supposedly have great penetration, but the surface of the weld left behind is so full of inclusions and slag i don't understand how you can weld over the top of a 6011 rod with something else without leaving inclusions.. unless of course you grind off the top of the weld.. which is probably what some people do.
6013's and 7014's don't have that problem because the slag cracks off on its own in once piece and leaves a relatively smooth bead.