Spent the last half hour or so doing some A/B action with the 4T's this morning...Grooooan...My job is so hard! 
Tough to add to what's already been said. Listened to some Norah Jones, Radiohead, Nirvana, Sigur Ros and others. In reference to Dan's post, I tried to do a lot of switching between the 4T's and 5B's. I love me some 5B's, but the differences were pretty vast in my opinion. "Don't Know Why" from Miss Jones had much fuller and "thicker" piano and the 4T's gave her voice more of a lifelike, in-room presence. The 4T also handled the upright bass more gracefully...Just more fullness and richness with tons of definition. Our demo room has no open space so all the sound stays put (as much as sound can do such a thing) and this was very noticeable in the bass. I double checked to see if our subs were on when i first got to listening...And as Caleb mentioned, the imaging is pretty amazing. Because we have multiple speakers in the room, I doubt that the 4T's are placed 100% as good as they could be, but Norah was still pin point centered in our smaller demo room.
Also listened to Nirvana's rendition of "Where Did You Sleep Last Night" from their unplugged NY sessions (one of my favorite jams from the group BTW). The strings had a richer sound with more body then the 5B's, and the drums sounded a bit fuller and accurate to the live performance. No doubt due to the fact that they have a more abundant midrange.
I hope that didn't seem like a 5B bashing session...As I mentioned for their size and cost, they are definitely one of my favorites. There's a reason that they get rave reviews from customers and professional reviewers alike...But if the extra $200 you'll spend for a pair doesn't scare you off, and you love you some music then the 4T's are definitely worth your while. I expect some great reviews in the future...
David Bolt
Aperion Audio Guru
www.aperionaudio.com