As far a I know, very few people have done the Rumbling-Lost John's connection, in fact I was told by someone a while ago its never been done since its original exploration in 1985, but I dont know how true that is - its very small, very wet and probably very stupid.
Cupcake is a new entrance which drops you down count lazlo stroganoff's aven in Notts II. From the Decent article a while ago it sounds like parts of the connection are quite difficult, which is why I suggested it. I know absolutely nothing about Voldermort, other than that its an entrance into Notts II, so I dont know how it compares.