For me, the thing that sets the Signature series apart from other high quality speakers is the tweeters. To my ear, they offer outstanding high frequency extension with an openness I have not heard on any other metal dome tweeter (except for other Beryllium tweeters).
Although modern Aluminum tweeters are much better than they used to be, they still have a component of distortion which can translate to "harsh" or "fatiguing", IME.
I think the Studio's Al tweeter is about as good as any, but when I listened to a Studio20 v.5 side by side with a S-2 v.2, I could hear some subtle "sizzling bacon" sound out of the Al tweeters, while the Be were open and clear. For me the Be tweeter offers the clarity of a soft dome with the extension of a metal dome - best of both worlds!
A good ribbon tweeter will get you virtually identical extension and clarity, but they are more sensitive to speaker/listening position. Whether this matters for you depends on your listening habits. If you listen consistently in the same position, a ribbon is a very good option.
But back to my main point, if at all possible, listen to any Signature speaker before you buy and make sure the high frequencies are "right" for you.
Naturally, the tweeter is not the only aspect to evaluate, but, IMHO, it is the biggest difference between the Studio and Signature series.
As Grant says, the more speakers you can listen to, the better decision you can make. However, you really need to listen to the speakers level matched in the same room to make fair comparisons. Inexpensive, but decent, speakers in a room which has very good acoustics will completely devour excellent speakers in a mediocre room!