The Nokia tablets (770, N8X0) are usually in landscape mode, and they then have almost exactly the same screen width as the 6" E-Ink devices in portrait mode. They are half as high though, so the line length is the same but twice as many page flips are required. Since the page flips are very fast, this isn't a big deal. Battery life isn't quite enough, but I was happy with my 770 as an e-book reader. E-Ink is better for most e-books, but the 770 really shines on SiFi Magazines with color illustrations. However, in this case the screen height is a limitation (in part because FBReader does not autoscale images).
I am still interested in a larger (than the 770) form factor tablet. Intel just announced that Centrino Atom devices must have 6" or less screens but there is no minimum battery life, see
UMPC Portal's report. I am really looking for something with a ~6" screen and a 5-6 hour battery life, but my guess is that a 2-3 hour battery is more likely.