Q6600(B3) can't get past 2.8ghz

Read the guides amigo. They help tons.

You are overclocking your memory and that is limiting your CPU overclock.

First thing, look for an OC guide for your motherboard. Combine that with this:
HOWTO: Overclock C2Q (Quads) and C2D (Duals) - Guide v1.6.1
http://www.tomshardware.com/forum/240001-29-howto-overc...

I am not familiar with the Asus BIOS, but somewhere in there is some kind of memory setting. Experiment until you find something that gives you a memory clock setting of twice the FSB. At that point CPU-Z should indicate a memory clock of FSB X 2 or 622 MHz. and an FSB:memclock ratio of 1:1.

We discuss overclocking RAM - or more accurately, why not - here:
http://www.tomshardware.com/forum/251715-29-ratio-myth

Then continue to work the FSB upward, increasing the CPU core voltage if you need to. Keep the core voltage under Intel's recommended max of 1.500 volts and keep load temps below 70 C.
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Overclocking since 1978 - Z80 (TRS-80) from 1.77 MHz to 2.01 MHz