What are the differences between the two from a practical standpoint. A little about my intended use:

I create acrylic equipment for the aquarium industry. Right now I am using a CO2 laser to cut 6mm acylic, and prep the edges with a router table before solvent welding. It is much slower, and I can't get consistent (within a few .001") dimensions, so every set is made as a matched pair (not interchangeable). Although, if I had a cnc router, I plan on working with thicker material and offering a broader product line. This is a high margin, small quantity business, so speed is not my primary concern. I am more concerned with edge quality, dimensional accuracy, and of course longevity of the machine. I seriously doubt I would run the machine more than 20 hours a week. With that in mind, is there much need for the IS over the Pro? Business is starting to pick up and as soon as I can justify it, I plan on getting a 4x8 3 axis gantry. I do this out of my home, so I do not have access to 3 phase, but I do have enough room left to add a few more 240V single phase legs. Finally, I have a standard height garage, would that height cause a clearance problem with a 408 machine?