What's the question? My bathroom is roughly the same size as yours with the same height ceiling. I put two 3" cans in the shower and 3 more in the bathroom itself. All use 50W GU10 bulbs. I have a box roughed in for a vanity light on the wall as well. With the 3 lights on its plenty bright but having the light on the wall will be nice for shaving, etc. The shower lights I need to put on a dimmer. They will be pretty harsh in the morning I think.
I think your plan of one can in the bathroom will either be too dim or look off symetrically or both, but I can't see your bathroom either.
The third light is just outside the frame here. I have two lights equally spaced in the shower of the center.