Best way to Sous vide two steaks to different temperatures
Pretty simple, cook the two steaks separately at the required temperatures the day before. Cool in an ice bath and reserve in the fridge. The next day rethermalise the steaks in the bath at say 55C: you really only need to heat them for around 25-30 minutes, as all you want to do is take the chill out of the steaks before you sear them on as a high a heat as possible. Do not season your steaks before they go in the bag because the meat will cure slightly overnight in  the fridge.

There's some good info on Cooking Issue around the cook/chill method, especially the pre-salting question:

http://www.cookingissues.com/2011/10/12/to-salt-or-not-to-salt-thats-the-searing-question/


  There are two main types of low-temperature cooking – direct-serve and
  cook-chill. For direct-serve you cook foods and serve them right away.
  For cook-chill, foods are cooked, chilled, stored, and rethermalized
  at service time. Here is a typical sequence for cooking a steak:
  
  
  Sear the raw rib-eye. This step kills bacteria on the surface, starts    the browning reactions that contribute to good meat flavors,
  and    ensures that a nice crust will be formed quickly later when the
  meat    is seared again.
  Put meat in a bag with butter.
  Cook the steak for 1-4 hours at 55 C. The optimum length of time    depends on how tough the particular steak is.
  
  
  Now, either:
  
  
  Pull the steak out of the bag, sear it (to make a nice crust) and    serve it. This is Direct Serve.
  
  
  Or:
  
  
  Chill the meat and store.
  Retherm it at 52 C.
  Pull the steak out of the bag, sear it and serve it. This is Cook-Chill.