OK, So...You don't want
A new laptop.
You want 2 New Computers.
My recommendation is to separate your processes. Put your Design on one computer and your control on a separate machine. Nothing worse than having to move a laptop around all day in the shop. Your cutting position probably wont be comfortable to sit at to design parts, and vise versa.
Since the plasma table is not really portable (your not taking it in the house) I would grab a cheap refurbished Dell desktop.
Something like this unit. This machine is should be fine for Cad/Cam/Control software.
You can build yourself a nice cart to mount it on. Pick for monitor (Touch Screen is an option, but not ideal in a metal shop).
The laptop is really a matter of budget. Cheaper laptops are going to be plastic chassis, with crappy hinges and don't expect more than a couple years out of it, until it just falls apart. Ive moved most of my customers as well as my personal machine to DELL XPS, they are pricey but have a all aluminum chassis with carbon fiber guts and have lots of options, Including upgradability (Ram/Storage) in the 15/17inch models.
Maybe this helps.
PS. I have 2 Computers in my shop at home (General use/Design, CNC Router) 99% of the time I design everything in the house in my office. All of my files are stored on the network so i can just walk out and open them up. I do the same thing at work, design in my office, save to the network cut in the shop.
