Yes, the four-door A3 Saloon is a little longer than the five-door A3 Sportback hatchback – measuring in at 4,495mm against the hatch's 4,343mm. The hatch is 5mm taller, however.
You get a fraction more rear legroom in the A3 Saloon and a 45-litre increase in boot space, up to a total of 425 litres. That said, the boot opening on the A3 Saloon is a little narrower than the Sportback's hatchback boot lid.