A tip we learned some years back (works for turkey also, as that meat can fall apart too). First, get a house brick of some sort, somewhere (Home Depot works fine) and wrap it in foil.
Cook a day ahead, any of the ways above are fine. For the corned beef (this part not for turkey), cool some, then cover with foil, and put the foil wrapped brick on it and put in cool/cold place overnight, refrigerator, garage (if cold winter weather). The weight of the brick and cooling will compress the meat some and make it much less stringy. Next day, unwrap and slice cold, slicing is a joy, so much easier than when hot. Then take the slices and reheat some in the oven (Marie uses some of the juice from the cabbage to give great flavor and moisten a bit.
As for the turkey, all the same except no brick. Cook a day early, chill overnight, slice cold the next day, reheat, use some of the juices from the previous cooking.
Enjoy.
I have to print this out for Marie for some new ideas.