True, but my guess is that the extra-genomic data, the preexisting cell, is a trivial amount, since it's always only interpreting the genome and is itself built

True, but my guess is that the extra-genomic data, the preexisting cell, is a trivial amount, since it's always only interpreting the genome and is itself built on an interpretation of a genome. Selection pressure has no reason to store a huge among of complexity outside of the genome after all. The bare minimum will do. As to how exactly that compares to the known 50MB, I've no answer but I'd guess it's an almost flat-rate amongst all species built by evolution.