Thiel 2.7 VS 3.7???

I am kinda torn at the moment and wondering if "anyone" has had a chance to compare these two speakers by chance?? I own and love the 2.7's and want to make the lifetime plunge and bump up to the 3.7 while I have a chance, but cannot get a handle by reading reviews if the main difference between the two is just in the lowest bass where I can possibly make up for by adding a sub or two?? I know there are probably other slight differences (Or major???) but have no way to audition 3.7's before I decide. I will either make the plunge and take my chances or keep the 2.7's. But thought I would check here first to see if anyone has any first hand experience with the two.