regarding the flex of the 37" span i dont think it will be a problem (at least i hope not the rails are very stiff) ill let ya know on the first cuts. regarding the Keling hardware i bought
there 2-425 oz-in for y and z 2-495 oz-in for x axis slave config and 5056 drivers the lead screws are 10tpi acme bronze nuts with my own antibacklash setup(hope this works too!!) i just botched my last motor mount gotta make another (chair)