You might take a look at my post on 12-01-03. If you're skiing 20 days a year, you have the right idea about rental demoing rather than buying. They may look macho - or goofy, depending on your perspective - but full fat powder skis are specialty equipment for special days, in my opinion, not much good for anything else.
In true pure bottomless ka-pow-wow, practically any boards on the market made in the last half-dozen years with a waist width of about 100 mm or better will work fine. Full fats don't need to be as technologically fancy as the latest greatest state-of-art hard snow carvers, and they aren't. There's more hot stuff out there than most of us can get around to demoing, but almost all of the off-piste skis I've tried lately are fun, once you adapt slightly to them.
For your average size and weight, don't go much over 180 cm length. At 5'-9", 160#, my ski of choice for the storybook storms - 20 days a year tops, of 100-120, even in the Wasatch and British Columbia - is the 2001 Fischer Big Six 106 (named for its waist) in 180 cm. I like the feel of a permanently cambered wood core, and its side cut, the shortest radius of any full fat that I know of. Other than colors, it hasn't been changed since about 2000 or so. On a guy my size, they resemble cartoon clown feet - after a couple runs of easy face shots, you won't be put off getting used to what you're seeing, looking down at those huge things sitting there on the lift bar...!
There are some skis out there that aren't for everyone, like people who prefer turns. An example of a ski that I'd be carefull about is the Atomic Big Daddy - stiff for a full fat pow ski, not to mention long, for those of us who have no reason to need a ski to handle, say, the run-out from a glacier cliff jump landing. For that matter, I've heard (and observed) similar things about the Stockli Stormrider. (But then, I'll admit, these aren't the only skis out there that alarm me just to watch some people on them...)
The slightly narrower, but still plenty fat Sugar Daddy is a more reasonable flexing ski, available without the plate in medium lengths. Also, I might've bought the Volkl Gotama, but a year and a half ago, if it even existed in the U.S. in anything under 190 cm, I sure couldn't find it. Now it's available in more normal lengths, I think it was 183-184 cm with a twin tip, makes it effectively under 180 cm running surface.
For buying - most of the time in the west, in anything much less than knee deep, especially after the snow gets skied up and crudded, you're better off with something mid to 3/4 width, waist in the 80's. My favorites are the Fischer Big Stix 84 in the 185 cm, and the Volkl G40, G41 or G4, 188cm, the last newest was the 7 24 AX4 (If I'm right, 2003 is the final year Volkl made these; a shame, one of the best all-around skis ever made.) Others - Volkl Explosiv, Blizzard Titan 8.2 and 9.2., Atomic R:EX, Elan Mantis 777, etc.
For lighter skis, the Dynastar Inspired and Intuitives (watch out for the Nobis models; again, long and stiff) and Rossignol Bandit 3X and B3 series are fun, but not as durable. Don't know much about K2 and Salomon's offerings in fat pow skis, but if the Pilot Series are as enjoyable as those cheap disposable X-Screams were, they're probably worth a try.
It's all about time and taste - cat skiing in the Sierras and in B.C., you're spending your time working on development of proper taste...!
Hope this helps...