I would avoid the electric carving knife if at all possible. I've had one in the past, and it just rips meat up (think "sawdust" when using a saw to cut would; here, you get "meat dust" LOL).
I'm lucky, working in restaurants. I have access to a meat slicer whenever I want to use it, provided I clean it up afterwards.
I've worked in several places that sliced their own Corned Beef for Ruebens. The first was a steakhouse, and they ALWAYS cooked their meat from raw. 8 oz of freshly-cooked Corned Beef on marbles light and dark rye bread, with all the classic fixin's......wait, that's another thread.
The last two places I've worked (currently still working at one) were both country clubs. One of those always used precooked, frozen, Corned Beef, usually made from Eye of Round. The GM there didn't like Ruebens, and would take them off the menu after a few months, but the members would gripe at him enough that those sandwiches would return after awhile.
The club I'm currently working at has done both methods, buy raw Corned Beef, cook and slice it, or just buy precooked meat, and slice it. It just depends on whatever is cheapest at the time.
Dang, now I'm getting hungry for Ruebens. I may have to buy a flat, take it to work, cook it, chill it, and slice it, then take the sliced product home to make sandwiches. Probably get enough for a couple day's worth of sandwiches (my other half, PeppA, and her mom, both love Ruebens).
Peace, Love, and Vegetable Rights!
Eat Meat and Save the Plants!