what is your favorite varietal or regional pairing for this dish?
TIA

Favorite? Everytime I have a Beef Wellington... uh... let me think... probably the middle of the last century. Like I don't indulge in it often enough to have a "favorite".

You want to taste and feel the three different parts of the Wellington. Traditionally it is made with a cut of the filet which is not all that flavorful. The pastry adds texture. The paté is probably the most flavorful part of the preparation.

That said I would try a lighter style French Burgundy or CA. Pinot noir. I would certainly stay away from and "big" wine.

I would agree with that also DJ. Just stick to the lighter-bodied (which I understand is not atypical for southern Rhones) with some good acid. The BW is kind of a complex dish all by itself and the acid will really prepare one's tastebuds for the BW's tastes.

Going with David's thoughts about good acid, I would go with a Burgundy or a cru Beaujolais (this is beef country in France). Domestically I think one of the "fresher" (as opposed to "riper") Central CA or Oregon Pinot Noirs would be appropriate.

I think a lighter Burgundy would be the best pairing.

However, I think the Duke of Wellington would be delighted if he thought any good French red was being ravished to serve with this dish.

the reason why i'd go with a southern rhone blend is to take advantage of the garrique type notes that would help accent the duxelle in the beef wellington - which is your primary flavor (or at least what i'm usually eating and leaving everything else behind).

a burg would also work...

would agree
am going to open on Christmas with a Wellington