The Intel Turbo Boost is a feature that will increase the processor speed automatically when it is needed. It works with internal algorithms and it also depends on other necessary things such as the ambient temperature, work load, etc…
My best recommendation at this point is to test the feature in a supported operating system (windows versions).
In regards the restarting issue, I recommend you resetting the bios settings and updating the Bios and Management Engine drivers. You can download the drivers at the following link:
The BIOS update fixed the first of the two problems: Turbo Boost works now
I get now the expected Multi-Core Score 4500 points: N/A - Geekbench Browser
(how to update NUC BIOS: just download (File name: WY0022.BIO), put the file on USB stick, while in the VisualBIOS you can select Update, a window pops up and you can select the .BIO file and start the update.)
I assume Turbo Boost mode works because I read that MHz increase up to 2.6GHz is not shown in e.g. cat /proc/cpuinfo.
I also have the feeling the NUC boots faster now.
2nd problam is still there: when I select turn off it shuts down and starts up again (Ubuntu 13.10).
I am sorry to hear you are still having problems but let me do my best to help you.
Based on the information you have provided, have you checked at the bios level if the fast boot option is enabled? I totally understand you are increasing the speed in the system but we strongly recommend using the default settings and a supported operating system.
Don't worry, I didn't over-clock or something, just BIOS update. Latest Ubuntu supports Haswell. For better open source graphic drivers one may install Updated and Optimized Open Graphics Drivers : Oibaf
2nd problem discussed here: NUC Haswell reboots after shutdown