Hold on! Andreas skis in the East. Here, the dominant need is to hold on hardpack/ice -- I too ski east. At 250 lbs, I use 63/64 mm underfoot. We don't need no stinkin' floatation!
The equivalent float chart from physicsman would suggest that at 20% more weight, you'd use a ski that is 20% wider, so your 76 or 77 mm to my 64 mm. But, if you don't need floatation anyway, you simply won't miss it. And a 76 won't turn like a 64!
If you are bowlegged, P. Keelty's site realskiers, has suggested that narrow skis are better, since you won't have to move your knees inside so very far to get the inside edge to engage. Another point for the narrow skis.
The key IMO, is to be honest with yourself -- if you ski eastern hard packed groomers 90% of the time, nothing is too narrow. If you really like spring conditions, and ski them alot, then floatation starts to matter. On the odd occasion, when the slush is bottomless and/or really heavy, I demo to get the float. To me, those are surprisingly few times, and IMO, do not warrant any real attention.
If you take one trip out west per year, and ski the rest of the time in the east, buy for the east and rent in the west. You'll probably hate wide skis on hardpack anyway. If you want to carve short radius turns, the ski needs to be able to do that -- forget about the 90 mm boards, you need the turning radius. Same with the 76 mm boards. If you want to turn on a dime, nothing beats the narrow waisted carver.
As for boots, mine have both hard and soft settings. They are set to soft. That is very conservative. Just because I CAN flex a stiff boot does not mean that I must have stiff boots! Stiff boots will transmit all of your movements to the skis, whether that was your intent or not.... IMO, boot stiffness is more accurately tied to skier ability and aggressiveness than it is to weight. Weight does play a factor, but it's highly over-rated.
If it was all just about weight, you'd be in a race boot on a real stiff and wide powder ski. Oh, since it's east, lets suggest a race boot on a GS plank. Either way, it sounds like completely wrong advice to give an intermediate.
IMO, weight is tied closer to ski length than it is to stiffness. 170 is certainly too short for you. I tried the Head ixrc at 172 and it was quite fine for me on hardpack. But, I wonder if I would push the tips too deeply into softer snow? I did with Elan 662's at 168. Fore/aft balance becomes a real issue when on short skis in softer snow.
If you ski blazingly fast, then sure, you may want the extra support that the stiffness brings. That being said, I prefer my boots set to soft, and like to ski blazingly fast -- but I can't keep that up all day long..... The downside to really stiff, is that errors you make in trying to maintain balance end up moving your skis about -- not what you want when you are going really fast. The downside to soft, is that really tight corners are much tougher at high speeds....
In the end you have to decide what to buy, and you should try to match the conditions and your ability. Big = Stiff and Wide is not an automatic decision.
That's my 2 cents. Hope it helps!