I don't think that window will be too large. The window in our smaller bathroom is 2'4"x4'6". That bathroom is larger than yours, but the window is in the toilet room, which is small. I think many people make the mistake of putting small windows in bathrooms. It throws off the look of the exterior, you can clearly tell which is the bathroom window because it is smaller (and usually shorter).

I just installed a much larger window in the newly remodeled bath, and I don't have any regrets about it. It wasn't an intentional install--I was willing to go a little bigger, and the contractor purchased a 42"x42" window on clearance. My old window was maybe 30"x32". I decided to go ahead with it, and I really like it. My bathroom is only 7'x8'(aprox.). The window looks great from the outside--it doesn't mess up the sight lines at all. From the inside, the window provides so much light.

The only thing is mine is not quite opaque enough, so the neighbors probably get a peep show sometimes.