Reversed 80 Planar gives me about 1.6x magnification. I get around 3x magnification on the reversed 50 but I'm not entirely satisfied with the performance. I don't see myself wanting more than that for 6x6. As it is, it requires exacting technique to shoot at these levels of magnification.
I'm experimental by nature - if I can squeeze some more resolution out of the enlarging lenses, they're worth a try. If not, just as well since the Zeiss lenses will be a whole lot easier to use!