I doubt that fall-off with different units is consistent as there are different mechanisms used to even out the light, and some units don't even try to even it out. Some NuArc units I have seen had a piece of glass under the bulb that was patterned to even out the light, others have plain glass.
At one time I owned a NuArc 26-1k and the fall-off at the far corners was about 1.5 stops as I recall.
Thats quite a lot! I am getting fall off with my exposure unit with twin 300w mercury bulbs on 11x14 inch prints. Am i likely to get with 1k unit?