Depending on your what your parts contours or internal holes / cutouts look like, you may be better off with a punch machine. I am pretty sure that you can punch 1/8 aluminum faster than you could cut it with only a 2000W laser.
To be honest with all the different manufactures I have worked with Trumpf is the best all around machine for punching or combo punch / laser systems. I have no opinion on a stand alone laser systems, however if your set on a laser to cut aluminum I would go with 4000W.
Independent CNC Programmer