The ThinkPad Twist is certainly Windows 8-ready since it was released as a new machine designed for that OS just after the Windows 8 launch.
I personally own the Vaio Duo 11 and like it a lot. The slider is strong and I don't think you need to worry about the slider components underneath the protective rear baffle unless you have kids or cats that might be tempted to reach in and try to pull the cables out.
The Vaio Z does not have a touchscreen and it ships with Windows 7. It's a lovely and powerful ultraportable, but if you want Windows 8 and a touchscreen, it isn't the right one for you.