G'day
From what I understand as far as depth goes on all the pi machines is that the depth is similar with all models, that is depending if they are used in the same soil conditions of course, but what has improved is the sensitivity to smaller nuggets at depth, and the ability to handle the hotter ground conditions, the use of the enhanced or fine gold settings can quiet the machine down to a level that allows you to hear deeper targets more clearly without the background chatter, but that can be a trade off of maximum depth as apposed to a clearer signal response.
cheers
stayyerAU