I've seen wide beds twist just as bad as a narrow bed does.
Wider bed give your cross slide more movement.
A deeper bed (height wise) gives you more vibration dampness.
More ribbing, especially "X" bracing give you more stiffness from twisting.
A double ribbed bed as found on Lodge & Shipley lathes, gives you a bed that practically will not twist or bow on you on long bed lathes.