My 920 is very, very bright at the highest settings. The 900 stays brighter when viewed at an angle, but when looking head-on I really can't see any difference.
What I appreciate a LOT when comparing it to my 900: It is much, much faster to adjust brightness as you go in and out of direct sunlight. My 900 would *eventually* look great in sunlight, but it sometimes took several seconds to brighten up, and I even had to turn it off/on sometimes when entering bright sunlight to get it to do so. (It also would take its sweet time to dim when going back into shade, but that bothered me less)
The 920, on the other hand, responds almost immediately and the difference, pardon the pun, is like night and day in terms of responsiveness and overall I prefer it. (In addition to all the other reasons I like the new display more...)