I think that 4 inches is a good compromise between the giant 4.3 inch screens and the smaller 3.7 inch screens. I have been messing with my wife's new Sprint HTC EVO 4G the last few days while I wait for my Sprint HTC EVO 3D to arrive and the bigger screen is really nice. I was surprised at the weight of it though. It is obviously heavier than the Sprint HTC Hero.
Hey, you could always have an AT&T Samsung Infuse 4G. That thing is 4.5 inches.