I am running on a pretty old machine these days. I7-3770k and a GTX 660 TI.
I set the graphics all the way down (it still looks good), and on the non main accounts I use this ingame setting /console set renderscale 0.4, to revert it back to normal you can change it to 1 instead of 0.4 or mess around with that number, it helps further squeak out extra frames but looks like a potato.
I'll upgrade one day, but this has made it less of a need.