For me the sound it was engages you into the movie, wrapping around you and generating the emotional response.
They are both important as the director spend a lot of time on designing both to give that full movie experience.
But then it is a personal thing, but remember a medium size screen with a matching size sound track will give a better over all movie that a big screen with a small sound track, it will just not feel right. Imagine going to the local Odean and then having a Getto blaster at the front playing the sound, would not really be the same. I know that is an extreme example.
All that said you do not mention what you are going for, it maybe that in a normal size UK lounge the sound system you are going for will fill the room and support the screen?