I wouldn't go any more than 56" personally.
And if you do go with a 30" deep tank I hope that the entry to that room is wide! Especially if using a ghost overflow. The tank will need to sit 4" to 6" off the wall so it will block a 3' opening easily.
I'm guessing that with SCA you will pay $600 more to get the synergy overflow cutouts and the extra 6" depth when compared to a standard 120g. You would likely only add $200 more to that to get from 48" long to 54" long.
Ehh, I think the entry there is wide enough... lol. Only reason I'm considering a 30" wide tank. That's my empty dining room. It was furnished until my ex and I split. The dining room set was hers, I haven't needed to replace it just yet. To the left of that entry way is where my TV is on about a 7' section of wall and there is another entry of the same size to the kitchen on the left of the TV. The kitchen and dining room are connected as well. Plenty of room to move around.
The tape measurer is set at 36" and against the wall. Plenty of room.