The macbook air is an attractive suggestion.
Have you tried using one in live view?
I do use a P45 and a P21+. The "Live View" on these backs is a joke. Simply unusable (at least for me).
I shoot, control the capture on screen, adjust something (if required) and take a second shot. This is also much faster than fiddling around with the so called "live view" on these old-school digibacks.
Often I shoot on CF card and when I think I have done the shot, I load the captures to the computer and check them before I pack in my equipment.
Mostly I don't use the computer at all... only in case of doubt. But the small MBAir is so light that I carry the laptop now more often than before ...