How different is a modern compact (C-Segment) car from a mid-sized (D-Segment) car?

Compact cars are getting larger every generation. There are some compact cars that are as large as smaller mid-sized cars. For example, the Octavia or Golf Variant is almost the same size as a BMW 3 Series. I would guess it doesn’t matter that much for driving in the city, so are they really that much less comfortable for longer trips? How different could the noise levels or general comfort be?

As a side question, what’s the comfiest hatchback you know that isn’t that expensive compared to a Golf?