Okay, so PEG is probably referring to the integrated graphics, but it doesn't matter, it's not relevant to you.
If you upped the BCLK to 125 immediately, I find it hard to belive you done very much reading before overclocking. The 3570k will have a multiplier of 34, 34x100= 3.4GHz. Upping the BCLK to 125 straight away is near enough a 1GHz overclock, without touching voltage or multiplier apparently? That's far too much. It makes sense that you wouldn't put at a BLCK of 125, or 110.
First thing I usually do is find out how much voltage the CPU will be comfortable with, then dial it back a bit and find a multiplier that works with the given voltage, then you can tart to tweak BCLK if you wish, but BCLK overclocking will overclock your RAM as well.
But yes, upping the BCLK from 100 to 105 is an overclock. Whether it was successful or not is another story, the system might not be stable under load. 105 on the BCLK is only an OC to like 3.6GHz though which is lower than the turbo speed of a 3570k AFAIK, so that would be fine at stock voltage unless you had a really shitty chip.