You have to take other things into account, not just a larger screen. A large screen is great of course, but if you can't see it in the daylight conditions you mostly fly in, due to it not being bright enough, or the fact that it may get too hot in the summer and **** down, then that larger screen area is useless because you won't be able to see anything or it simply wont work when you need it. A larger screen also means more reflections in it, so if it is not bright, in bright sun it will be very difficult to even see, since it may well not be very bright and it will be showing you far more reflections than that smaller phone screen was, that you once used.
Therefore, when choosing a screen, I would say the brightness is the first thing to consider, then the functioning of it, will it easily over heat? Then the cost and how it integrates with what you have. Remember, it could be the best in everything you always wanted in a screen, from size to weight to cost to cool running temps but if you can't really see it in the bright sunlight you usually fly in, it won't be of any use to you.