I have more bags than anyone on the planet, and given your situation, I think you might want to take a look at the Moose Peterson bags here:http://www.moosepeterson.com/gear/index.html
I have not used one because other people have said that they don't have much padding (maybe none), and I like some padding because I'm a klutz. The minimal padding is apparently an effort to do exactly what you need, i.e. provide the largest carry-on bags with the least weight. In effect, your high-tech camera-specialized garbage bag. Moose says that he's traveled lots of miles with the things, and never a problem. Of course, what else would he say? 8-)
I've carried laptops for more miles than I care to recall, and guess what? Lighter is better. You can cut a lot of weight off that 6 pounds you're talking about, although you'll give up screen size and perhaps some other functions. If you're stuck using Mac, then you're stuck. If you can use Windows, Sony has some really good, really small laptops complete with DVD burners and reasonable hard drives. They are not much good, however, for heavy-duty word processing.
Speaking of which, when I travel, I now carry a lightweight keypoard and mouse in my checked baggage. It's all on wheels, so I don't really have to deal with the weight too much, and a keyboard makes a big difference. I've also bought keyboards when I'm going to a city with easy access to a computer store, and simply tossed them when I left. You can get a keyboard for $30, which is small change compared to an airline ticket.