I,m no expert on this but i,m sure it will bend.
The reason i say this is because I cut my gantry end plates out of a piece about the same size, so going on that i think it would bend.
I suppose a lot will depend on what you intend to put on it and what tolerances you intend to work. If it,s just wood and the load is spread then no probs i would think, but if your putting engine blocks on it the thats another story!!
Easy way to tell would be too support both ends put dial gauge on it in the middle and then load it with something a bit heavier than what you intend to cut.. . . .I think you might be surprised how much it moves.
It,s an easy fix thou, just add a brace down the centre on the underside. . . Simp-pills. . :-)