As Gunnerbob suggested, weight shouldn't be the primary factor for down sizing a ski. In downsizing, you'll be reducing the weight by a small amount, but also dramatically changing how the ski performs for you. If you skied the 180cm and loved it, then stick with that length.
In terms of the Bonafide vs. Kabookie, the big difference to consider is their stiffness. As you might now, the Bonafide contains two layers of metal, while the Kabookie has none. So really the debate between these two skis, should be settled over how you ski. Both the Bonafide and the Kabookie are excellent expert level skis that handle a range of conditions and terrain quite well. The question to consider though, is how aggressively you approach advanced runs. If you consider your style to be more finesseful, meaning you take your time and perhaps perform a lot of hop turns, then the Kabookie would be an excellent choice. If you're more of an aggressive straight shooter who likes to find his way to the bottom ASAP, then you're going to want a stiffer ski with you to handle more intense situations.
Both skis are excellent, and are highly capable of East Coast skiing. You won't be making tight slalom turns on hardpack days, but you'll be able to make it from top to bottom with no problem. I definitely don't see these skis as being too big or burly for east coast conditions by any means. Really, you've just gotta make the call on how aggressively you ski, and how stiff you need your skis to be.
Hope this helps!
Matt @ Skiessentials.com