Is this tenderloin safe to use?
This is a really, really tough case.  From a strict interpretation of our canonical answer for such food-storage questions, the answer is unfortunately: no. This cannot be considered safe according to the guidelines used by the FDA and other food safety agencies. It's impossible to know exactly what temperature the beef reached and for how long, so this must be considered suspect.

From context I'm guessing that you're cooking this at home, but you cannot and should not serve this in a commercial setting, period.

Now, here's where we get into strictly my opinion. You must evaluate your own consideration of the risks involved.  

If you are certain that the refrigerator reached no more than 42 degrees F then I think that the risk presented is relatively low.  8 pounds of beef has a decent amount of thermal mass, and assuming that it started closer to 35 degrees F and was properly vaccuum-sealed I think there's a good chance that it never crossed into the danger zone, and most likely wasn't there for long if it did.  FDA guidelines are famously conservative (for good reason, as they're designed to reduce risk for everyone!) and to me that's a rather expensive cut of beef to just throw away.

I wouldn't feel comfortable serving this to children, the elderly, the pregnant, or anybody else with a potentially compromised immune system. Remember that food poisoning is no joke and can be fatal, especially for such at-risk people. You may want to reconsider cooking this for the holidays and serving it to your family. But I'd probably be comfortable eating it myself if I was certain of the conditions that you describe. You may justifiably be less comfortable, and the FDA would back you up. If you decide to cook and serve this, you must do so with an awareness of the risk presented.