Nowadays they usually underclock their chips to fill all market segments, because their manufacturing process is too good to produce enough slow chips.
My 1.86GHz Core 2 Duo runs at 3.5GHz. Almost 100% overclock. The fact that it's (or was) the absolute lowest end chip helped. This is not an exception. Almost everyone who has the same chip reports achieving similar OC.
RAM is especially susceptible to thermal failure because it's essentially a big array of capacitors. At higher temperatures (say 50C), capacitor leakage increases, limiting maximum frequency.
