Depends on several conditions. There are two different clones which will build extreme big (perhaps even the biggest) pitchers,but within these this also differs if grown under different condions.
So the biggest that I´ve ever seen are the show plant "Howells´Giant" from David Svarc and "Eberhard König" from Matthias Maier. As far as I know Davids´secret is a bigger pot every new season,while Matze feeds his plant with Osmocote (maybe David too,but don´t know about that). Apart from that they´re both grown under greenhouse conditions,but I´m not sure anymore in which soil.
But however,both clones can reach a much bigger size than Dudley Watts.