Added steel channel to X-axis c-beam

[wiremonkey]

So, here is my current plan for the X beam, 2" x 6" x 3/16" steel beam with linear rails. I'll weld at least .25" thick plate onto the ends for mounting to the gantries. Maybe thicker? Not sure if it's necessary, will just add more weight.
Over on the Openbuilds forum, M90Ranger suggested I split up the rails and use a design like this: Certainly two .25" wall 2" or 3" square tubing would be cheaper than the single 2" x 6" I purchased. Somehow I like the overall feel of the single rectangular tube. Which do you think would be more rigid?