You do plan on replacing the wood supports for your table? With all the effort you have gone into getting your machine to this point, I would replace the wood with some extrusion or even some square steel tubing, then mount your MDF top on that.
Wood is just too unstable for use as a table support. Another option would be to use electrical conduit struts (available at most home centers) sandwhiched between two pieces of MDF.
Author of: The KRMx01 CNC Books, The KRMx02 CNC Books, The KRmc01 CNC Milling Machine Books, and Building the HANS Electric Gear Clock. All available at www.kronosrobotics.com