Thiel 2.4 or 3.6, which to get?

Hi all,
I have Thiel 3.5s and really like their sound, but am on the horns of a dilemma. I have been thinking that my next step up would be to find a pair of nice used Thiel 3.6s, but have run across a pair of dealer demo 2.4s which have never been sold and which I can buy for $2300.00. The dealer who has them in his warehouse is very open to letting me audition them at my home, but is a two hour drive (one way) away from me. The idea of having new speakers with the full warranty appeals, but driving four hours to get them and possibly four hours to return them if they are not a substantial improvement over my 3.5s, plus the roughly $1000.00 additional cost over some nice used 3.6s, (if and when I find some) gives me pause.
So, althoughI have gotten some helpful input from a previous post regarding this issue I am hoping for more or new input from Thiel knowledgable 'Goners because I actually need to make a decision in the next few days.
If the feedback I get here is that the 2.4s are a substantial step up from the 3.5s and at least a noticable step up from the 3.6s I will pull the trigger, take a day off work, do the driving and pick them up for an audition.
What I like best about the 3.5s is their transparency, detail, soundstaging and bass. More of these characteristics is what I am hoping to get in any upgrade I make. All inputs from folks who have actually owned or heard these models will be greatly appreciated.
Thanks!