My opinion is that the gantry is heavier than it could be. If it were me, I would go larger in cross section and go with thinner walled tubing. The lighter and more rigid the gantry is, the less power it takes to move it around and the less inertia it has to overcome. You can engineer in more strength without adding so much weight.
In comparison, a steel framed tandem bike designed to carry around several hundred pounds comes in at 56 pounds. That is with a span of around 5 feet.
Again, just my opinion, you should easily be able to get the structure of a 2' long steel gantry down in the 10-12 pound range without breaking a sweat and still have enough stiffness to carry your mechanicals, spindle, and cutting loads.
My uncensored views and CNC Router planning: http://reinventingcnc.blogspot.com/