Very good Tara, you are much more articulate and thorough than I am.
Coopers, don't forget that White can be made on ANY e-series PLUS there are Partridge Chants out there floating about with only a single dose of eb Brown, the other allele in the e-series is often eWh (shows up when the pseudo Partridge is not expressing the diamonds I so cherish). It is not PROBABLE but certainly possible for then the White to donate an eWh and the pseudo Partridge to donate the other required eWh.
Yes, white is the wild card here. Is it not possible to 'guess' what the white may carry from the history of the bred? I have actually seen some 'sports' from whites that have an interesting mottled, greyish pattern in them so there may be a pattern gene lurking in there.
I had what I am sure was eWh show up in one of my birds. He was very light in chick down with very little striping. He grew to a very orangey male with no black in his hackle or saddle. Looks like I may have some eWh lurking. I think I got rid of the hen I suspect had it so I am not to worried.
He was a BIG boy and tasted GREAT!
So I suppose it is possible and my short 'nope' was wrong, but why would you want to go through all the trouble and heart ache it would be. I was thinking along the terms of 'if I crossed whites with partridge, the chicks will be buff' and not 'if I spend years breeding, documenting and culling i will have buffs before I die!'
I would just go out and buy them.
I think why you ask is because you have both and want to breed them together. Just do it, you will get lots of people that will be appalled, but just doit and see what you get. I know I for one would be very interested to hear what you hatch from it. I have always been tempted to experiment with it myself.
Oh, Tara I think the buff wyandotte and buff brahma in Australia may be on eb or at least eb/eWh. I think the standard down there calls for slate down.