Remove the tenderloin from the refrigerator 1 hour before cooking.
Combine the sour cream with horseradish, using more to make it stronger. Season to taste with salt and pepper. Cover and refrigerate until serving time.
Preheat the oven to 475°F. Rub the tenderloin all over with olive oil. Season generously with salt and pepper. Place in a roasting pan, insert an oven-proof meat thermometer, and roast to 130-135°F for medium-rare, 20-25 minutes. For rare, roast to 120-125°F; for medium, 140-145°F; medium-well, 150-155°F; adjust times accordingly. Let sit for 10 minutes before slicing thinly.
If desired, brush the cut sides of the rolls with olive oil and toast lightly in a skillet. Serve the rolls with the sliced beef, sour cream sauce, and arugula.