This may be no help, but my only experience is with 160 stud Nokian Mount & Grounds. This is my second winter on them and my impressions are:
1. They absolutely rule ice. I can't even imagine how Extremes, Freddie's Revenz, etc. can be any better, but I have to assume they are.
2. Deep snow is hard work. I think this is an axiom across all winter tires, maybe the only exception is those double-wide rims with 4 inch wide tires run at 9 psi or whatever.
3. So if you accept that a reasonable amount of studs tames ice, deep snow is hard work, then the natural conclusion is that all of the difference in studded tires are subtle gradients between ice and deep snow. Since the tread works the snow and the studs work the ice, there's probably some point of diminishing returns on number of studs unless you're racing across a Minneapolis lake. That said, I'm going to order a pair of Freddie's Revenz to put on my 2001 Hoo Koo E Koo Disc just to see what Winter singletrack is all about.