In reply to The New NickB:
I was bored so c&p'd this from carwow.co.uk. All relate to the saloon versions of the cars:
Octavia: 4659 (L-ext) x 1814 (W-ext); h'room: 983 (f) & 980 (r); boot space: 590L; w'base: 2686
Passat: 4767 (L-ext) x 1832 (W-ext); h'room: 989 (f) & 964 (r); boot space: 586L; w'base: 2791
Superb: 4861 (L-ext) x 2031 (W-ext); h'room: 1004 (f) & 980 (r); boot space: 625L; w'base: 2841
Unfortunately they didn't seem to list all relevant internal dims, which are probably the most useful stats. What was most surprising to me was how much wider the Superb is, at least externally.