If I recall, your room is a relatively narrow 4m (13ft) and relatively long at 8m (26ft).
However, the details of the room matter. If you have a large screen that forces you to shove your speakers into the corners. Floorstanding speakers are not going to like this even with a Subwoofer. So, the little details matter. You have to think of the entire room combined with the equipment as a single system. Each decision will effect the other aspects.
With the room only 13ft (4m) wide an on the assumption that this is were the screen and equipment will be, you don't have much space. If we trim 3ft off each side to make room for larger speakers, then that leaves a 7ft space in which to place the screen and the equipment. That still leaves room for a pretty large screen.
Further, not only do the speakers need to be away from the Side Walls, but they need to be forward of the wall behind the speaker, by how much will depend on the specific speakers, but you can count on at least 1ft forward.
Most Movie systems will want a Subwoofer, especially if you are into Action movies, though personally, I don't use a Subwoofer, but I have FOUR Front Speakers, which means I push considerably more air than the average system, and as a result am able to generate considerably more impact. Though my room is only 16ft x 16ft (5mx5m), the entire spaces is 16ft x 36ft (5mx11m), so my large speakers have plenty of space to unload into.
Also, if I recall from your other thread, you have a very considerable amount of money to spend ... very considerable. Give that, I would say that you give some serious consideration to Room Acoustics, with that much money on the line, you want to make sure you get your money's worth, and Acoustic Treatments will help toward that end.
A couple acoustic panels placed at the point of first reflection, perhaps some bass traps in the corners, and a combination of acoustic panels and diffusion on the far back wall should do the trick at a very reasonable price. All this combined with the Room-EQ that any modern AV Receiver is likely to have, and you should be able to do very well.
With what I interpret as your budget, you could even call in an Acoustic Consultant to make recommendations for you about room treatments.
More than any one factor - you, your preferences, your circumstances, your room, and your budget - are the determining factors.
Steve/bluewizard