Quote Originally Posted by Voicecoil View Post
How about a variation on "C", bring the 2 80x80s close together (ditch the crap collecting gap) and plate them front and back to make say a 90 something x 160 section? You could even slip a drop or 2 of epoxy where the extrusions meet if you were feeling keen
Doesn't need to go that far because there's more than enough strength in profile, he'd just be adding weight. The epoxy would just be a waste of money and offer nothing in terms of strength.

If he had a little more length and could afford slightly wider bearing/gantry plates I'd suggested going with 160 flat with 160 on top and with rails in same front and top positions. You have to think about the direction of cutting forces. The wider bottom profile makes the gantry stiffer in the direction of cutting forces.