How large is your room? If you have a larger room, go with the Arc. Even without the two upward firing drivers, the Arc is still a much larger and better sounding sound bar for TV and movies. Not counting the upward firing drivers, the Arc has nine drivers compared to the Beam’s five drivers. Also remember that Dolby Atmos audio is more than just height channels.

Is the above consider large?

Your room is large enough and suitable for the Arc. And even if you had flat ceilings, the 3.4 m distance you are seated from the Arc wouldn’t allow you to really hear the upward firing drivers anyway.

Will it make a difference by me adding a Sub with 2 One speakers to the Beam as compare to just one Arc setting?

Yes, adding a Sub and two One SLs as surrounds to the Beam would be a dramatic improvement over just the Beam alone and probably slightly better than the Arc alone. But if you have the budget, I would still go with the Arc and then add the Sub and surround speakers to the Arc later. The Arc just produces a much wider soundstage than the Beam.

If I were you, I would purchase both options and test them both so you can hear the difference between the two. Sonos has a good return policy.

Thank you for your insight.