You just need to enable Turbo Mode(M.I.B III– Performance Tuning – CPU Configuration – Turbo Mode => enabled) to over-clock. However, please understand. About the over-clock of Turbo Mode, the over-clock range is depended on how many CPU cores active.
If the program you run only need to active one core for high loading, the over-clock range will be large.
If the program you run need to active all CPU cores, the over-clock range will be smaller.

For example,        
You can see detail below from Intel, about  i5-2500K ,
when active core is one, the max Turbo Boost Frequency will up to 3.7GHz.
If active cores are 4 cores, the max Turbo Boost Frequency will up to 3.4GHz.
on my side, I used “CINEBENCH” tool to make CPU high loading for single core to check the Turbo mode.
 


Related models : 
P67H2-A (V1.1)      P67H2-A2 (V1.0)      P67H2-A3 (V1.0)      H67H2-A3 (V1.0)      H67H2-I (V1.1)
H67H2-M (V1.1)     H67H2-M2 (V1.0)     H67H2-M3 (V1.0)     H67H2-M4 (V1.0) 
 

Yes, this model with UEFI BIOS can support 3TB HDD. UEFI BIOS uses a GUID Partition Table (GPT) that can define hard drive larger than 2.2TB. As a bootable disk over 2.2TB partition, operation system like Windows 7 64-bit is required to support. For data only over 2.2TB, OS with GUID Partition Table (GPT) support is required.

Example, 
3TB HDD as data in GPT at Windows 7 :


System support UEFI BIOS GPT table:


3TB HDD as data in MBR at Windows 7 :



For more information about GPT&MBR partition, please refer to
http://www.uefi.org/learning_center/UEFI_MBR_Limits_v2.pdf
http://msdn.microsoft.com/en-us/windows/hardware/gg463525.aspx

This model may has concern on the S3 or S5 wake up by certain USB keyboard or mouse to the EZ Charger USB port. It means that you may have possibility not be able to wake up the system from S3 or S5 by the USB device. This is because the USB EZ Charger port provide 3 times current than general USB port for consumer products like iPhone, iPad and iPod touch that need large amount of current for faster recharging within less time. To avoid this kind of symptom, please attach the USB keyboard and mouse to the general USB port to obtain the expected behavior.



- More information for EZ Charger,
http://www.ecs.com.tw/extra/ezcharger/index.html