lars888888,
At 8 ft the CS 2.4 is your best choice. It is a steal on the used market and the upgrade path Thiel Renaissance has planned will make this model highly competitive in the 20-25k speaker realm.
The two issues, already discussed, that creates problems with the larger Thiels is power (amp) and room (integrating). If you get these right the CS5i will keep a smile on your face. Look at the You Tube CS5i on that site. Look how close they are to the walls and the ceiling.
My setup is 10.9' tweeter to tweeter, 3.3' off back wall, 3.6' off side wall, and 6.5' to ceiling.
If you feel at any point you may get a larger listening room then I would jump on the CS 5i and hold on to them. As Tom eluded too, improving the 4 electronic crossovers and a handful of other improvements Tom has mentioned in this thread is well worth getting a pair.
On an aesthetic note I love the Mid Century modern design that the CS5i embodies more than any other Thiel speaker. When I have the CS 7.2 next to the CS 5i they look short and plump in comparison to the sleek and elegant CS 5i. World class craftsmanship.