According to the Starship Dimensions site that Khai referenced, here's the sizes of some of the ships mentioned:

Star Wars Destroyer - 1.6 km
Silent Running - 1.6 km
Battlestar Galactica - 610 m (after Star Wars)
Enterprise - 305 m
Discovery - 113 m
Eagle (Space 1999) - 68 m

I don't think the old "When Worlds Collide" ships are in the listings, but I don't recall that they were as large as the bigger ships here.

There's no question that "Star Wars" owes a lot to "2001". That movie still holds up well today with effects that remain realistic. John Dykstra, at least according to IMDB, didn't work on "2001", but did work on "Silent Running", which was directed by Douglas Trumball, who was the effects director on "2001".

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon