I haven't heard either, but I've heard people here say
a) The 100s have deeper, tighter bass(than the 60s, that is, to be expected with the 3 7" drivers vs 2 6.5" drivers).
b) The 100s, along with many other paradigms, have an upper bass hump not present on the 60s or 80s.
c) The 60s/80s have a bit over the 100s in the mids, rest is similar sounding.
And lastly, while sound quality between the two when compared 100% opinion - looking at their prices, I'm sure it's a fact two M80s would sound better than one Studio 100.