I suspect that we'll see Nicola on the next one, as Peri spent more time with Six than Five, I think (and she still looks damn sharp, IMO).
Well, the only Sixth Doctor serials she wasn't in were the last two of the overall "Trial of a Time Lord" arc, so I doubt they'd show them. It'll probably be something from Six's first season. I think my vote would be for "The Two Doctors." That's probably his best, even aside from the Second Doctor's appearance (it is by Robert Holmes, after all).
I'm watching "Earthshock" now, and there was a scene where the Doctor was giving a long expository monologue rather quickly and urgently, and I realized I was reminded of Jonny Lee Miller's delivery as Sherlock Holmes on Elementary