I used 55mm/4.5 on 6x7 for this impromptu group shot. I was probably around f:4.5, so the people on the edges and toward the front are a little fuzzy, and there's some subject movement, not to mention closed eyes and unfortunate expressions, being one of the last two shots that I had. I'd say I was about 16 feet from the front row set up in an elevated vestibule off the room where the rest of the family was. At least I had a tripod and Delta 400/Acufine. I don't print it larger than 5x7"--
So I think if you go small format, you can be around 24-28mm. If you shoot 4x5", your 90mm should be fine, if you stack the group right.