Nina, your welcome.
Think about what's happening when you SV cook.
Heat is slowly penetrating meat.
Do you have a ruler? Probably won't do. You need to be precise to be successful. Consider that a 3-inch thick piece of meat will require 50% more SV cooking time than a 2-inch piece because it is 50% thicker.
Think about it.
I know this isn't an easy concept to grasp when you are new to SV cooking. The heat energy penetrates the meat evenly from all around, unless of course your cooking vessel is too over crowded and there's insufficient water circulation, but you wouldn't do that.
To calculate the SV cook time required you need to use the lesser distance heat travels through the meat. The 5-inch depth, or length, of the meat could be 10-inches. Cook time won't change, only thickness matters.
Think about it. What is happening as the meat cooks?
Ok then, split the difference temperature wise and cook for 3 to 4 hours, but no longer or you will be unhappy with your result. For your guests who prefer medium-rare blot their meat slices heavily as you slice them. That's how to have rare beef tenderloin appear medium-rare. Also, if you are serving a pan sauce, and i recommend you do, serve the sauce beneath the rare portions and over the medium-rare portions. That way you won't have a who-gets-which-plate mix up or have to conduct an annoying table side who's the rare? plate auction.
If you're not sure about how to go about making a pan sauce avail yourself of one of the Knorr Demi-Glace mixes and make it ahead using only about half the water so the meat liquids in the bags can be incorporated into your sauce. You would be surprised at the number of restaurants that use them as a quick, consistent, and easy solution.