Overclocking I5-4670K@4.5Ghz.. But its decreasing clock speeds

I am trying to squeeze more out of my CPU till now i was using@4.4 GHZ with the AI Tuner but i have read many times that manual overclocking is best
So i am trying to Achieve Stable 4.5Ghz what i did is i have set the
AI overclocking profile to Manual
Core Ratio Limit 45
CPU Core Voltage Manual Mode
CPU Core Voltage Overide - i tried at 1.23 in the screenshot it was set at 1.23V but after 5 min of prime 95 PC Hangs so now while typing i set it to 1.24V

I dont know its correct settings or not
you can see in screen shot
the issue i have is while running Prime 95
the CPU is not getting Hotter as it should be Running @4.5Ghz and randomly the CPU speed is dropping to 2.5Ghz or 3.9Ghz that i dont understand
Please tell me what i am doing wrong

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