I finaly got it working in 1080p.
Current graphics Driver: 10.18.14.4170
What did the trick was very stange: I installed hyper-v.
After you installed hyper v connected standby or any standby at all is not available anymore.
make sure to apply this workarround to get connected standby working while having hyper v on your machine:
I am connected agains a Samsung LE46C570 in 1080p now.
Works only with the smaller 32 Inch Version of this tv now.
Bluetooth is active, bt devices are conneted and i use a 2.4 ghz wifi connection.
For the Moment it looks like it works as it should now.
will Report if it stops working.