20x8??? 40x8??? I have never seen anything. Does something bigger exist? I know about the tft screens but they take too many pins. I like the 20x4 with i2c. Very easy.
Search on eBay. I think 40x4 shows up sometimes.
40x4?
Or go with something besides LCD character display.
nixies? 
Need a lot of nixies for 4x40 characters!