I have a 12" Power Book G4 and could not be happier as it is light weight, reliable, great for photographic downloads and editing, excellent Firewire support for video input, etc. However, it does not have a PCI card slot so you would need to opt for the 15" to use Sierra/Verizon wireless network cards.
I carry a spare, always charged battery to deal with the long flights plus a power box that works on aircraft power outlets and auto power outlets (formerly known as cigarette lighters).
I run Virtual PC on it for remote access to a corporate network and it has never failed me for wifi or hotel network access connections anywhere in the world. Log onto the network in OS X then start Virtual PC.
Virtual PC loads up and shuts down reasonably quickly. Other than ie and the Java scripts my remote access requires, I do not run PC programs.
Tried to load up some Windows games using Virtual PC for my son on his mac, a bad and disappointing experience given the hardware reguirements of high end PC games. I could not get Rise of Nations to work, for example. Except for my son's game envy, I have not had a need to supplement my program needs with non-Mac software.
Good luck with finding your "universal" solution. I found mine.