One other effect lowering temperature may have is to alter the relative effects of different developing agents. For instance, hydroquinone becomes virtually inactive below about 60F, effectively converting a two-agent developer like D-76 into a single-agent developer (in this case, similar to D-23). This may have a disproportionate effect on fog, because different developing agents produce more or less fog. Metol and more so phenidone are generally low fog, but they aren't usually used alone because they're too slow and low contrast -- but hydroquinone, often used with one or the other, is a high fog developing agent as well as producing higher contrast.
Now, whether ascorbate (generally a replacement for hydroquinone) has the same properties in terms of losing activity abruptly at a particular temperature, having high general fog, or being a higher contrast developing agent) is the question if you're using Xtol or other ascorbate developer. Contrast I think is a given -- else why would ascorbate replace hydroquinone in developers? Fog and activity curve with temperature, I don't know for certain -- but this is worth looking into before trying cold development with an Xtol-like developer.
