Are you making sure the board is good and high (angle wise)? Im a crappy inexperienced carver, and i can't apply nearly as much as i know, but from what ive heard and the little i have done cranking the board high on its edge is the way to control the steeps.
There is one thing i think i can relate to you on: im the same weight as you. I'm on a 162 and for me it turns pretty wide unless i crank it high and downweight with everything ive got. I had Pogo give me a slightly softer board than their usual Overdose, fearing that I wouldnt be able to turn a stiffer board at all, and im glad i did. but I think i still underestimated my need for softness. Id say try softer boards. Many guys on here are closer to the 200+ weight range, they can bend their boards like a wet noodle.
For stability at high speeds, length sidecut and stiffness all play a part. Its too complicated for me, I tried to figure it out and I just gave up:smashfrea
And the conditions you described are probably the most difficult carving conditions. the only way they could be made worse is if a few new stumps and rocks decided to shoot up, somebody sprayed everything with a hose and froze the entire run, and an entire busload of senior citizens skidding down on straight skiis decided to use that run at the same time. (but you know that already)