For notebooks, higher clock speeds kill battery life. If you max out on power-hungry options, even those that don't weigh much, it might mean carrying an extra battery, and that's a lot of extra weight. Screen size isn't an easy choice, either. Everyone loves a big screen, but it can make the notebook's footprint so large that it won't fit in a suitcase. So, biggest isn't always best.
Many notebooks offer similar performance and features.
Your purchase decisions could come down to vendor reputation and the bundled software. The latter is negotiable, so some systems in the chart are listed with extra software and, because many agencies will install their own licensed programs, some aren't. There hasn't been much improvement in run times because, as batteries get better, performance, and thus power consumption, goes up just as quickly. Lithium ion batteries perform best. But when considering your choice, look at milliampere-hour and voltage ratings and not at vendors' estimated run times.