I'm pretty sure that the B-Squads are stiffer than all the all-mountain twins in that range.
I did some similar research a couple months ago. Head's Mojo 105 is reckoned to be the stiffest of the all-mountain twins. It comes in a 181, which would be more than enough ski unless you're (a) huge or (b) good-sized and crazy-aggressive. The Gots and the Prophets are next in line.
If you don't care about twin tips, you might check out the K2 Chiefs or the Dynastar Prorider Series in addition to the B-Squads. They're fairly stiff.
If you plan on turning much, doing technical lines, or going into the trees, I wouldn't advise going with a too-stiff ski though. There's a good reason why pow skis tend to be softer.