Remember that E+ is not an upgrade, it's just seat selection. As a Silver, you may select at check-in. The question will be whether what is left of E+ at check-in is better than what you already have. E.g., do you really want an E+ middle over a decent E- middle?

As a Gold, you have an equal shot at E+ as a GS. You may select E+ at booking.

UG's to F are a different issue. Predicting those on a systemwide basis is impossible. Route, day of week, time of day, time of year and so forth will dictate the answer to that. General probabibilities won't help you here.