Don't know what you mean by the PSC rear bar but I just asked Genright this question (alum vs steel) when I ordered the aluminum version a few days ago. I was told there is no material difference between them except that steel rusts and alum does not and price, steel is $100 cheaper. Maybe weight is a factor to some. Steel 73lbs, alum 53lbs, only a 20lb difference. Both are equally strong - built to handle 42" tires/wheels. Both install in the same manner. I also noted on their webpage that the steel version is available black powder coated, alum is not. I ordered the alum carrier from Northridge 4x4 but was just told the alum is out of stock and would take 2-3 weeks to deliver directly from Genright. Will ask about steel availability today when they open, if steel is available now I will change my order to steel. I think the carriers are normally shipped bare (no box) so I would not get powder coat since that would probably raise the price a lot since it would have to be boxed to protect the paint.
I want to use PSC (or Genright) rear corners but neither Genright nor PSC has ever installed the Genright carrier on PSC or Genright corners so they cannot tell me whether the combo will work well or not. So far no replies to my earlier post on this forum asking if anybody has used this combo and how it works.