Not rare. Medium rare plus. 
We like our tenderloin very rare; one time after everyone was served, one person said “I’m sorry…but…could you please throw this into the oven for just a few minutes?” DH said, “sure.” About 3 more guests said, practically in unison, “Well, as long as you are doing that, can you take mine?” 
Yes, really the key is not to overcook it. Ours was delicious. We took it out at 135 degree internal, tented it with foil and let it rest for 10 minutes. It was perfect. Not a morsel was left. Thank you for all your help. I now feel more comfortable about it for next time!
@VaBluebird Did you choose to the slow or fast cook method? Glad it turned out well. I think it is intimidating at first just because it is expensive!
We had a 5 lb. for Christmas. My H put some olive oil on it, then some garlic, salt, pepper, and rosemary. Fast method, served with horseradish cream sauce. It was delicious and we had it the next night as well. And a lille left over for sandwiches for the day after that.
I learned a technique a few years ago that is foolproof. Rub a 3 or 4 pound tenderloin all over with 2 tsp kosher salt. Put in fridge UNCOVERED (,to dry out surface and force brine into meat) for 24 - 36 hours. Remove from oven 1 hour before roasting, and rub with olive oil and 2 tablespoons freshly cracked peppercorns. Roast at 425F until center is 125F. Let rest 15 minutes, then slice.
We used the fast method. 425 degrees for ultmately 40 minutes, rested for about 15. A 5 pound piece.
The moans and groans of approval proved we nailed it, LOL.
Those of you who cook whole tenderloins regularly: how much uncooked weight do you allot per person?
We had a 5.21 pound one for Christmas for 5 people . But all but my sister had seconds. We also had enough for dinner the next night, also a little left for a couple sandwiches for a couple of people after that. I think, in general, maybe allowing a very generous .5 pounds per person. I would think a typical 5 pound tenderloin should feed 10-12 people comfortably . If you are serving other meats, lots of additional stuff as well though, then the tenderloin would serve more people.
We buy a whole beef tenderloin at Sam’s Club and ask the butcher to trim it. Of course you still pay for the whole loin (including the trimmings) but don’t have to trim it inexpertly yourself.
Costco sells a “peeled” tenderloin - about $7 more a pound but no waste. I usually buy a 5 pound one - should feed 10-12 easily.
We get ours at Costco too and do nothing with it in terms of trimming anything.
Doing the slow roast now using the “surround roast” setting on my big Miele oven. Will let you know how it turns out! 
Holy JPMorgan, that is a nice setting!!! It did the job in less than an hour using the Ina Garten’s directions in the link someone posted earlier (thank you!) - good thing I checked early or the meat would have been overcooked! Evenly cooked throughout, Mr. enjoyed his dinner. Steak salad and sandwiches tomorrow.