Paradigm is one of the brands that I like quite a bit. They were my "top of the line" before I got introduced to the wider world of audiophilism.
I definitely would consider the SongTowers an upgrade over the Studio 20's. Its kind of apples and oranges though, because its a monitor vs floorstander type of deal. So right off the bat, you are going to get another 15Hz or so extension by making the switch, which I think is going to give a more complete and satisfactory music experience. Note that I'm personally biased towards the towers, I gave up monitors some years ago.
The studio 20 is good speaker, but I like the Salk sound myself. The SongTowers are just so deliciously smooth and have really good clarity. They have excellent bass punch for the size drivers they have. The high end isn't harsh. As an all around performer its hard to beat for the price. I know some people don't like Paradigm because they say they sound harsh on the high end, although I was never one of them. But on the other hand, I don't know that I've ever seen anyone describe a SongTower as being harsh.
There are quite a few owners in the northeast, I'm certain one will pop up. I'd be interested to hear your impressions after you listen. For me, something like Salk means I won't go back to Paradigm (that and I have no more money), but for others, maybe the difference isn't to their liking.