MK4 cabin is very similar to the MK3, distance from the brake pedal and the rear backrest is still 211cm and also the boot lenght is moreorless the same (2 cm less for the MK4, 65 vs 67cm). MK4 wheelbase is 1cm shorter due to suspension geometry, but thanks to thicker bumpers MK4 Crosstar is 9cm longer.
The bigger difference comes from the front seats position, 5cm rearwards, so driver and front passenger can have more legroom, but rear passengers will have less.