I shoot both formats as well, but just use a modified dark slide to get two 4x10 negs on a single sheet of 8x10 film. I do not use a wide angle much, but will occasionally use a 165mm and a 210mm with 4x10, otherwise I use the 300mm. For distant panoramic views I have used the 19" with 4x10 (and even a 24").

A two-lens kit for me (using it on both formats) would be the 210 and the 300. The first addition would be the 19", then the 165mm.

Vaughn