From an artistic(non-gay *scowls) point of view. I would go with iCafe's wife's suggestion. The first pic in his post. Just raising the larger painting in the center a bit. I do like hippo's suggestion, however I feel it makes it look like the paintings are being hearded. Having the larger picture in the center draws your eyes toward it. I suppose if you had a picture showing more or maybe a different angle. Perhaps showing how that particular section of wall connects to the other walls, that would help me decide.