Without getting into true telephoto design, your camera will support 500 mm at infinity. Less then that if you do any close up photography. Myself, I would not consider much above 400 mm in a non telephoto lens for the reason of close up bellows extension. This would give an equivalent of roughly 130mm in 35 mm.
With a telephoto design, different then what I was addressing above, the focal length could be increased but in telephoto designs focusing considerations as relates to lens standard tilt changes. They are more difficult to work with, for that reason, in my experience.
Which lenses? That depends on whether you are buying new or used. The Nikon Tele designs are popular. I like the G Clarons in Schneiders non tele designs, tons of coverage and sharp as a tack at a fairly reasonable price.
Also, you'll want to keep issues like the size of the shutter and such in mind. Your Wisner can probably handle anything in a Copal #3 shutter, if the rear lens cell fits through the front frame and you don't mind carrying it around, and maybe even an Ilex #4, but probably not anything in an Ilex/Acme/Betax #5 shutter. A long, fast non-tele lens might be heavy and difficult to work with, but slower lenses like the G-Clarons and Fujinon-C or older Goerz Artars are relatively compact.
Though tele designs can be a little less intuitive to work with as far as tilt goes (because the optical node of the lens is actually way out in front of the physical lens), what you lose in sharpness due to the design compromise inherent in teles, you might gain back in camera stability (at least if you are not using a two-tripod arrangement or extra stabilizing arm), because they don't require as much bellows extension.
We will have several G-Clarons with us this trip. If the lens boards don't fit your camera we can always mount them on our cameras and your can use your holders to make images. That will give you an idea of longer lenses in 4x5. I am very partial to the G-Claron group. They come in a 150 mm 210 mm 240 mm 270 mm 305 mm and a 355 mm. As David said, they are little and sharp as a tack. But the are slow. They are all f:9's. But don't make any commitments until you see these lenses.