Cook it at 450f for the first 20 mins then drop to 325f.
At 1hour and fifteen mins I would check the IT every 15 minutes till done rare.(prolly 1-1/2 to 1-3/4)
Do not salt until cooked, baste the exposed ends.
Rest at least 20 mins
Merry Christmas!
^^^^Yep, go with buc's advice, sounds about right for that size roast. Perhaps guidlines have changed, I usually go to 120-125 IT and remove from heat, cover with foil and hold for about 20-30 minutes for an IT around 130 for rare.