If a filet then Med rare.
I've been going rarer and rarer with the Sous vide though. One thing I always hated with rare steaks was how bloody they were. When Sous Viding steaks, that problem has gone away but I can enjoy a nice tender tasty steak.
My wife used to be a well done shoe leather girl. The Sous Vide has gotten her to Medium and she's even done medium rare a couple times.