Something to consider is what aspect ratio you plan to use for the image, as viewed by the user. Here's what I mean. If you take an image with 1:1.5 aspect ratio (like a 35mm camera) and you plan to display the image in as an 8:10 print, then you are going to need to crop the image, which means that your image is going to look like you used a longer focal length lens. I won't go through the math right now, but the general implication is that, taking the aspect ratio of the final print into consideration, if you want something with an angle of view equivalent to let's say a 85mm portrait lens as used in 35mm, you would need about a 340mm lens in a 4x5 camera. You could get away with a little shorter lens in the 4x5 because you might want to give yourself a little more freedom to crop the image just they way you want it, whereas in 35mm you might want to crop "in camera" taking into account that you are going to shave off quite a bit of the image along the long-dimension in order to make the enlarged 35mm image fit onto an 8x10 print.