I have never tried to cook a tenderloin as large as yours but, for a tenderloin/eye fillet about half the size, this is how I would cook it:
Tie it up so it is an even thickness for the whole length (in other words make sure the tip is tucked under and secured), rub with salt and pepper, wrap it up tightly to set the shape, refrigerate for a few hours, remove the wrappings and bring to room temperature, and then sear well on all sides (including the ends). If you are crusting it with mustard and herbs or something similar, do that just before you put it in the oven.
I would preheat the oven to 475-500 degrees Fahrenheit and when I put the meat in (with the rack positioned at the center height), I would drop the setting to 400F. Cook about 15-18 minutes TOTAL (not per pound) till it registers 120 degrees internal temperature for rare (I would take it to medium rare personally - to approximately 125 degrees) and then let rest for a minimum of 15 minutes tented before serving. You may have to adjust the timing for a larger cut of meat, especially if it is thicker rather than just longer than a smaller one might be but I would expect it to be more done than rare if you cook it for 15 minutes per pound which is what you say you have been told it needs.
If you don't have a thermometer (they are cheap and I recommend you get one before you cook this because you have an expensive cut of meat and don't want to ruin it, I would guess!), then I suppose you could gauge the doneness by pressing the meat as you would a steak or cut into it a bit to see if it meets your desired results.
