Does picking a scab make scarring more or less likely? i've read arguments for both outcomes...i'd like to know specifically for a rather deep cut.

I vote for...: More likely. With a typical scab, that is nature's way of helping the cut heal. There are some occasions when a doctor will remove a scab and clean out some dead cells and other goop in the wound, to let healing restart in a fresher way... but that is the occasional situation. Usually, a cut heals better if one doesn't pick at (and pull off) pieces of scab every day or two.