It's not just the components that come into play with machines. The case and ventilation are very important with machines that will put out a lot of heat when they are put under the stress of high CPU and graphics usage. Gaming and CAD-level portables are meant for this as they have the ventilation designed into their casework in order to maximize airflow. I know because I own an older (4 year old) Alienware M17x. It's an I-7 based machine with 8GB of RAM and comes with an ATI 5970 discrete video card. The case is aluminum and has vents all over, both back and front as well as the bottom with multiple fans to pull the air in and heat out. It still runs TS12 quite well, although the disk space is quite small, sadly. It was a large disk back then, but you know how hard disk space goes over time...Anyhow, the biggest trade off for heat dissipation and an aluminum case is weight. The machine is a beast and weighs close to 15lbs.
The other consideration too, outside of heat, is discrete video circuits. With machines, such as the Alienware models, the video card is not strapped by system memory. Like a desktop machine, these have a separate video card which can be replaced should this one give out. They are merely plug-in modules that go into a small socket located on the bottom of the machine. This too has its own fan to allow for proper cooling.
The Dell XPS 8100 is similar to the Alienware M17-series and shares much of the same components. Remember to keep the air vents clean otherwise it will cook and degrade the components.
John
