The NEX 5 is a great camera for mapping since it records good geotags as well as taking really nice imagery. We have been converting people over to the Alpha series due to gimbal availability issues. More pixels is not always better, but the Alphas will do a great job. The main issue is their lack of GPS tagging... But if you have a method you like for inserting geotags or are OK doing the manual georeferencing, they should be great.
Another camera to consider is the Alpha 7s. The 'S' stands for sensitivity. It is only 12 MP but those pixels are huge. This gets you a much shorted integration time for your images and results in less smear when you are flying on a cloudy day or late in the day.
Ground smear is likely affecting your images more than you think, especially if you are flying fixed wing aircraft.