I'm going to be shot down for saying this, because it goes against all accepted wisdom on here - but you should give very serious consideration to a Redbay Stormforce 850 or 950. The hull was designed specifically for fast operations in just the type of waters you describe - in their case, off the west coast of Scotland.
They are not as fast as a Scorpion (with the same powerplant) in calm water but when the boats have been run side by side in the rough, the Redbays have maintained higher average speeds. It's difficult to know if that is down to the helm, but my guess
is that the Redbay has a more forgiving hull. I've put in hundreds of miles* in these craft (8m-10m+) and am just off the 950 that completed the Round Ireland 2013
course in fairly poxy weather conditions.
They build completely custom craft, so can create whatever layout you require - the hull is wide enough to accommodate three jockey seats abreast.
This is a concept for one with a "cabin" - with outboards instead of diesel, it would have space for all your PAX.
*Just totting it up - it's over 1200Nm so far