Have always been steaks and grilled. Not sure I should say more since I have no experience with it roast style, but its me right? So we know that is not going to make a difference.
I would cut off a steak if feasible, and test cook just like you have posted. Now, will a 8-12oz. steak be the same as a 3-4lb.(?) roast, well...should give you an idea at that low of a temperature...you should be able to see if it seems 1) to much smoke when taken to that IT and 2) dried out after the sear at that IT.