Well I use my tablet to draw images that are A4 and larger. The point really is how often you draw one stroke from one side of an A4 page to another? If you are not doing large strokes like that then you don't need your whole image up on the screen. You zoom in on the area you are working on and the tablet will map very well to that region. You then move the window to the next piece of the image and work on that. I've found no issue with working like this. It just allows you to zoom out on the image for doing the rough sketching and then zoom in when you work in the detail.

The one issue I can see with the smaller tablet is that you can't really trace anything that is larger than the drawable size without some careful jiggling but I don't trace stuff so its not so much of an issue for me. Hope that makes sense.