Hey chat, thanks so much for your points here, let me see if I can remember the more specific details here:
This was a totally "visual" assessment, meaning that the color was "the usual" deep pink-red I see in steakhouse-cooked meat, so I was inclined to say that was not a matter of cooking time/temperature.
My 131F/1h20min was also eyeballed by saying, "ok the recommended temperatures should be around 129°F-134°F for medium rare, let's do something reasonably in between". I had no reason to actually choose one value over the other.
I don't know the specific thickness, but I would say ~1.5 inches.
This is actually a great point. In my case, experimenting with SV means also experimenting with searing, so I also bought a cast iron skillet. I usually bring it to the smoking point before searing the meat, which I think it would be kind of aggressive, but from what I read it might have taken a bit too long with respect to the 30-45 seconds I read being the standard timing.
I would say it took me around twice as much, slightly less than two minutes for each side.
Maybe this is the point...
I bought the meat from a big supermarket in the Boston area, which I don't have reason to complain about and from which I have usually bought meat I was satisfied about when grilled.
Thanks again for your suggestions, I will try again!