Consider getting a good used system and budget for a new battery -- battery life on used laptops is a (loaded) coin toss. If you are price conscious you will likely get a better value than from a cheaper new one.
On choosing the model for a portable -- IMO the #1 goal is to get one with physical characteristics that work for you (size, weight, monitor, keyboard, ability to be a tablet, etc.). CPU/Memory/storage is a very distant second. Go to a store and hold many models in your hands. If you work next to other techies, ask to see their travel computer option; ask for advice. This will likely give you a lot of honest info and demos.
Extra 25% of CPU speed will get you little benefit if your ultrabook is not comfortable for you to work on.
On choosing the model for a portable -- IMO the #1 goal is to get one with physical characteristics that work for you (size, weight, monitor, keyboard, ability to be a tablet, etc.). CPU/Memory/storage is a very distant second. Go to a store and hold many models in your hands. If you work next to other techies, ask to see their travel computer option; ask for advice. This will likely give you a lot of honest info and demos.
Extra 25% of CPU speed will get you little benefit if your ultrabook is not comfortable for you to work on.