Have you ever used a significantly larger phone because if you had, I'd suspect you would feel this way. In fact, having a longer phone is actually MORE detrimental to one handed use than wider.
I also have a Galaxy Nexus which checks in with something like 4.6". Contrary to the popular argument by the iPhone faithful, it's not two big to be used or carried comfortably however I do feel it's pushing the limit, especially for one handed use. The problem though isn't reaching across the screen but rather reaching the top of the phone. The top of the phone is already further from your thumb than the opposite side so just adding length is going to make it even harder to reach. Sure, the keyboard is at the bottom but trying to reach anything on the top is a stretch (i.e. notification bar).
Personally, I'd like to see 16:9 aspect ratio but do so by increasing both length and width as required, ideally to the 720p found on the newest Androids devices--4.3" seems ideal, IMO.