After experimenting with larger e-ink screen sizes from other vendors I realized I also miss the snappiness of reading a real book. So in the end I settled for the cheapest 12-inch Chinese tablet I could get. Since I spend ca. 40-70 minutes a day reading, it's the best experience for me: the text is crisp, the contrast is perfect, and I can browse pages very quickly (not like in a real book, though, but the best experience so far).