That can be a pretty pricey bottle to drink with those steaks- the Mouton that is, though it will stand up nicely to them.
One thing to watch for on buffalo is that even the most tender piece can still be as chewey as an onglet- I try to do a deep seasoning with salt and pepper on mine. Enough of that.
Let me suggest a Pinot Noir that I think is a bit softer than the Mouton and will work really nicely with a simple preparation (you'll be surprised at how inexpensive it is compared to the Mouton, but it's ready to drink right now. This is also something that while ready to drink now could use a year or two in the cellar to make it really top quality). Patton Valley (OR) 2003 Pinot Noir. Yummy.
Also, for a Cab Sav with some real muscle take a look at the vertical selection available from one of my favorite producers- Cathy Corison (Corison Vinyards). Get a bottle (any year) from her Kronos collection. I especially like the 03.
I've got a bottle of 93 that I'm going to break out tonight from the regular napa vinyard.
is making all his reservations under the name Steve Plotnicki from now on.