We were on a six cabin Saba 50 last summer. Generally we had nine people on board, but for a couple days we had 13. It seemed a fair bit smaller than the Lagoon 520 we were supposed to be on but still never seemed to crowded when we had all 13 on board. The middle two cabins might be a bit tight, but the other cabins seemed about normal for a 45'+ cat. They were perfectly adequate for sleeping or to get away for a few minutes. The saloon is pretty functional for a large group and there are plenty of places outside to spread out. People tended to congregate up at the steering station and on the front of the boat when underway. No one hung out much in the cockpit until we were at anchor or tied to a slip. I would have no problem chartering a Saba again for a large group. Also, although you said performance wasn't a concern, the boat sailed relatively well. We typically sailed at a casual 7-8 knots in winds of 12-17ish and got it up to double digits several times once the wind came up. Not bad for a loaded charter cat with a big crew.

Have fun!

Matt