I never faced random reboot, freezes, hang ups, auto shutdowmns etc already using the phone close to 2 months .
OC and UV do cause hanging, freezing - random reboot not sure. This you just have to test yourself - start from a low UV level and monitor. Some users hat XDA has reported certain UV levels not recommended. I didn't read into their details as I just UV what I think is best for my purpose

Random reboot are also usually due to 3rd party apps especially those warez from blackmarket. I don't overclock at all - 1.2 Ghz is more than enough. Using SetCPU, i set the range from 500 Mhz to 1.2 Ghz and I also set profiles for screen off, temperature above 45, charging, battery below 30% - to control mainly my battery usage . It is amazing what these tools can do in combo with Tegrak app

Repeat again : for Tegrak I just undervolt CORE Voltage  75mV across all levels 200 Mhz to 1200 Mhz. Don't touch/change any of the Internal voltage figures

Setcpu : I set minimum 500 Mhz ; DON'T set it at 200 Mhz - phone might not wake up.
For all profiles this is what I set : Highest , Lowest, % priority
Battery < 30 % : 800, 500, 95
Display off : 800, 500, 90
Temp > 45 degree : 800, 500, 100
Charging : 800, 500, 80

It could be location. Have you try using Market Enabler?

1 question , did u use Chainfire 3D ?

-Edit - Nvm , not found unless I turn on Market Enabler

our sgs2 can use this? looks nice..