Here are the numbers wrt screen real estate differences, and a really nice visual comparison for anyone who want to get a feel on how the screen size differences compare.
http://www.displaywars.com/6-inch-4x3-vs-6,8-inch-4x3
For kpw owners, because I had it measured in mine, roughly imagine the top bezel (from the corner onwards) also becomes screen real estate, as does the right bezel, again from the corner upwards.
Another way to say this is, take out the L formed by the left and bottom bezels, and imagine the rest, screen included of course, as the new screen size, approximately.