If you do a little research on dry aging you will find that most "high end" steak houses age their meat for up to a month. That being said, the conditions need to be monitored closely, strict rules need to be followed, and there is very little room for error. I am not suggesting you to do this, just that it is possible. I purchased my 17 lbs (one 10.5 lbs and another 6.5 lbs) on Wednesday this week. I watched the butcher cut, dress and tie it while I waited, ran home and prepped it.
The final product is to die for and I have not ever made anyone sick. Once sliced and on the plate you can cut it with a fork and the beef flavor is about as good as it gets. If you can maintain the temperatures till Sunday I think you will be okay. If you keep it at 36 or below (constant) then it shouldn't be a problem. You mention temperatures in the low 40's........... That will not do. Be careful, getting sick on Christmas day would not be a joyful time.