OK, keep in mind that SkiPressWorld went out of business. And that any review site is not any better than it's reviewers; SPW's tended to like to rip. I would suggest Real Skiers for reviews that are more suitable for most intermediate to advanced skiers. (They also like Heads, incidentally, but also Blizzards.)
Second, Pre KERS Head SS's are not in any way shape or form similar in forgiveness to Blizzard Sonics. The two are vastly different skis, in that Heads are damp, heavy, love to turn turn turn, and stiffen a little as you flex them, so they remain planted at speed (a good thing). But they can become a handful at that speed if you're lighter (you never state your size) because they're stiffer yet than when you started turning. (Maybe not such a good thing). They are not the grippiest ski around and have crappy factory edges; you'll need to reset the edges at 1/3 to make them work on ice. I'd agree that you can learn well on a SS. I love them, I have owned a pair for years now.
Blizzard Sonics, from what I deduce (have skied the Supersonic), are light, lots of snow feel, much easier to initiate and move around, not as planted at speed, but more versatile as to turn shape, terrain, and lower speed handling. They also will have better grip than the SS's out of the box. A better choice for lighter skiers IMO.
So some of this is about who you are and what you're seeking in feel. If you like the Head feel, then pre-KERS SS's will be really fun, as long as you take lessons and respect their potential. If you want a lighter ski that's got a wider envelope for speed and turn shape (and will tend to ride up through, rather than plow through, soft snow), then the Blizzards will be great. Personally, for your purposes I think the Contact is the best of the three, and certainly the most versatile. They rock bumps, they do surprisingly well in light pow, and they will teach you to carve in a way the other two won't.
Suggest you STOP FOCUSING on specs like waist width and sidecut (I have no clue what a "better" sidecut even means). Just because your present skis have a certain width or sidecut doesn't mean that any ski near those specs will handle or feel the same, or that you have to change your specs to make the swap worthwhile. If in fact you want a more all-mountain ski, that will do better in a few inches of soft snow, but not as well on ice, then you should jump up to at least 75 - 80 mm waist and will probably end up on a longer sidecut. If you want that, I would strongly recommend last year's Head iM78, if you can find one, Blizzard Magnum 7.6, or Elan Ti78. Otherwise, pay attention to the feel, handling characteristics, and forgiveness of the skis you're looking at. See which matches your style and terrain you usually ski on.
Finally, do your homework here. There are excellent reviews of every ski that's been mentioned. Search.