I don't see why you would not push this build just a bit up and finish with aluminum cutting machine. I mean a very nice aluminum cutting machine.

I am in the process of making now exactly the same working area machine and one of the ideas is to cut Aluminum precisely. Ignore the third bearing blocks in the middle everywhere.

By pushing a bit up, i mean on the long axis 2510 screws from china and rotating ball nut . I am not expert here, before some time Dean told me not to go RP if i want precision cuts. You would not believe how comparably cheap are 2x 3m / screw + nuts, for what they will offer.

2x 100x100x4 for the gantry , 100x100x3 for sides , front and back. All rest cross sections could be 80x80x3

just received 7x6m 100x100x4mm which i will use on all machine. 500eur with transport here in Spain. So basically my design uses 42m of main material. It doesn't matter if you make it on the floor or raise the legs, its the same.

i am expecting from my machine 20000mm/min, servo driven 1:1.5 , with very good resolution. That at 3000rpm of the servos. Not that they can not be driven at 4500rpm. There were panasonic servos at ebay, that have the same torque up to 6000rpm. that should be pretty frightening though

if you want fast, and heavy you will drive it AC servo, yes? Not that it can not be step driven, though i cant imagine what i would feel if it looses steps when i am doing 2m ali sheet