Larry
I would bet vibachrome is in reality fuji flex, RA4 compatable - c -print,dye coupler print.
cibachrome is too hard to do for a very large lab therefore the switch to the RA4 product.
I use both here , ciba and fujiflex, once again I would state the cibas always shine compared to the fujiflex.
As far as stability , RA4 is a dye coupler process, verses cibas P3X dye destruction process, which one is more stable , ask me in forty years.