Successfully overclocked my cpu to 4.5 Ghz..Except

I successfully overclocked my cpu yesterday to 4.5 Ghz using this http://www.youtube.com/watch?v=WMZoWOpry40 video.

After the initial overclock I loaded my cpu for about 40 minutes at 100% using intel burn test. the highest one core reached was 79 c but that was only briefly. Most of the time 3 cores were hovering just below 70 and that one core was hovering in the mid 70's.
After some game time last night I decided to test it again this morning.
Instead of 3 core hovering just below 70 they are now in the early 70's sometims reaching the high 70's and the 3rd core that is always hotter than the rest is mostly at 78 79 c and even went as high as 83 a few times during the test.

So my question is should I try underclocking to say 4.3 and see how that goes? and what voltages should I use for that amount? and why after keeping the temps low yesterday has it decided to jump an extra 5 degrees? (the rooms temp is about the same)

cpu:- core i5 2500k
gpu:- hd7970
mobo:- ASUS P8Z68-M PRO
ram:- 8gb @1600mhz (corsair vengeance)
Heatsink:- Coolermaster hyper 212 evo.

Just as a side note the core temps at idle hover around these figures per core and haven't changed like the load temps
1:- 35c
2:- 25c
3:- 40c
4:- 35c

Voltages:
On this motherboard you are forced to keep the cpu and pch voltages on auto.
CPU voltage auto @1.260
DRAM voltage @ 1.600
vccio voltage @1.100 CPU PLL volatage @ 1.900
pch voltage auto @1.050

One thing I've noticed. The bios screen tells me that my cpu is still running at 3.3 Ghz, but my load testers (realtemp and coretemp) both tell me that the cpu gets to 4.5Ghz when loaded with intel burn test. Is this normal?
and whilst playing games the highest temp I see is 65c.

You will get more help if you post what you are overclocking.......Complete system specs including cooler would help. Also, I have no desire to watch a youtube video to figure out how you overclocked so including things like voltages would help too.

You're missing voltage info.

I have a similar spec. You shouldnt be running that hot with 4.5ghz. What voltage are you using?

Hmmm, I would bet that those voltages are going up when the CPU is stressed. I have not seen these chips going to 4.5Ghz under 1.3v, and if it was it would not be running that hot. Either that or you have a case with no airflow or your CPU cooler is not mounted correctly. You did use thermal compound when you installed it right?

Yeah man; like I said, The ASUS P8Z68-M PRO forces you to keep the cpu voltage on auto and the pch voltage on auto.
But that's the information I'm getting on the bios. The other voltages I set based on the information the video provided.