Using "The equation for the distance D between film and image as a function of lens focal length f and magnification m is D = f * (m+1)^2 / m."
For 8x10 negs:
300mm lens: 2 mag (16x20) 135cm/53.2" 2.5 Mag (20x25) 140.8cm/55.5"
240mm lens: 2 mag (16x20) 108cm/42.5" 2.5 Mag (20x25) 112.7cm/46.3"
My DR has an 8' ceiling. I use a Durst 184 with Pavelle head. I use 240mm, 300mm, 360mm, as needed, but the 300 is the default. I have printed 20x24 with a 300mm. My Max D = 66.5" so, I could, theoretically, get to 3x (24X30) with my 300mm! Platen low/head high!!