A laptop built for gaming is going to run you more than 50% more than what you pay for a desktop. If portability is that important to you, go for it, but if it ain't that big a deal stick to the desk top.
when you say "computer idle on high" what do you mean? Is the hard drive always spooled up? You might have a memory issue where the computer is hitting a "virtual memory" on the hard drive. Run the dxdiag and post the first third here (cut and paste the text file), also post what setting you use in the game, texture size and such.
