SuperShape (SS) Magnum and the SS Chip are the same dimensions and construction - only difference is that the Chip has the intelligence chip which, depending on whether you believe the marketing blurb or not, smooths out vibrations at higher speeds. I've skied both and felt that the SS Chip was "really" damp on harder snow at higher speeds. I loved it, although some (many?) skiers will feel that dampening a Head ski, which tends to be pretty damp to begin with, is overkill. I'd say you almost have to ski both models to say which you would prefer. I felt that skiing the Chip was somewhat akin to driving a Porsche Cayenne - smooth and very powerful. The Magnum would be more like driving a Boxster.
The difference between the Magnum and the "original" SuperShape is the dimensions. The original SS is 66mm underfoot with a 12.1 meter turn radius and the Magnum (as well as the Chip) is 71mm underfoot with a 13.5 meter turn radius. The Magnum has just a bit more width through the ski and is perhaps a degree or two better for all-condition skiing with just a bit more flotation for moderate powder and crud.
Both are really great skis. I'd say if you REALLY want quick, fast turns then you should select the SS. If you want a *slightly* longer turn radius on a ski that you might be a bit more inclined to take off-piste, then choose the Magnum. If you want the Magnum dimensions in one of the smoothest skis you've ever felt, then go with the Chip SuperShape.
This review might help:http://forums.epicski.com/showthread...ighlight=xenon
Good luck with your search.
disclaimer: Head gives me free skis.