I also set it to 3GHz with a cheap motherboard, even though it was a P35.

I don't know about Asus, but with my Gigabyte, there were multiplier ratios for memory and then it showed you the effective speed. Be careful not to force the memory above its specification, some motherboards show you frequencies but they are not the resulting ones, but multipliers. You can check the effective speed in CPU-Z.

You can also give it a little more power. Have you tested it? Look at the voltage that CPU-Z shows you and comment on the options you have in VCore Over Voltage.

Mine had a modest cooler and maxed out at around 60°C. I don't recommend reaching 70°C under load, but it would be fine if you could get close to 3GHz (300x10). In my case, I needed a little less than 1.4v if I remember correctly.

PD: To measure temperatures, you could use CoreTemp for example, or if that's the case, OCCT and you have monitoring of both voltage and temperatures. For testing, you could use Prime95.