Not sure about the actual physical display dimensions, but we do know the sq mm and pixel dimensions. Keep in mind, the 49mm refers to the height of the Ultra’s case, not the display size; and it also has thicker bezels.
49mm Ultra is 1164 sq mm and 410x502 pixels
45mm Watch is 1143 sq mm and 396x484 pixels
41mm Watch is 904 sq mm and 352x430 pixels
So the Ultra’s display is only 1.8% larger than the 45mm watch (or 21 sq mm and 14x18 pixels). For comparison, the 45mm watch is 26.4% larger than the 41mm watch (or 239 sq mm and 44x54 pixels).