The mistake is measuring the room. What matters is the space around the table: 90 cm from the edge to the nearest wall or radiator, or nobody can get past a pulled-out chair.
Work backwards from that. A 200 cm table needs a room 380 cm long to be comfortable, and 340 cm to be usable. If the numbers do not work, a bench down one side buys you 30 cm, because a bench pushes in.
Then measure the route in: the front door, the turn at the bottom of the stairs, the landing. Tables come apart and sideboards do not, and we would rather know before we cut.