In general, for re-sale, sight unseen, I think you are better off with the PSA card 2 grades lower. If I had a KSA 4 of Morenz or Joliat that I thought would cross to a PSA or SGC 2 I would cross the card.
The only instance I can recall where a KSA card will outsell a PSA is with the Gretzky rookie. A KSA 8 used to outsell a PSA 7, although I am not certain that is still the case.
I understand the difference between those 2 companies and their reputations. That's why I was very specific about KSA card being at least 2 grades higher. From my past experience on eBay the 1933 OPC Joliat PSA 4 was sold for $200, 1936 OPC Morenz PSA 2 for $375. For some reasons I believe that hypothetically Joliat KSA 6 and Morenz KSA 4 could go higher...Maybe I'm wrong.
I've crossed a lot of KSA cards to PSA and they are almost 100% of the time 2 grades lower, occasionally 1. The recent KSA 3s I've seen are poor quality 1s at PSA. I'm starting to avoid KSA unless its an issue I really want.
I've crossed over 20 cards from KSA to PSA after cracking them out of the holders....and experienced a .80 average reduction in grades. Also, one of my last 'regrades' came back from PSA as 'altered' so that slipped by KSA at first. These were not pre war cards though.