Overclocking greatly varies due to what hardware is being used and who is doing the overclocking. Always remember that no two pieces of hardware will perform the same, so our results will differ from what you might be able to get.
With stock BIOS settings, the AMD Phenom II X6 1090T processor runs with a 200MHz bus speed (base clock) and an x16.0 multiplier that is used to reach the final core clock of 3.2GHz when all the cores are at full load.
I was able to lower the HT multiplier and push up the Bus Speed to 250MHz in the BIOS for a rock solid overclock of 4GHz on the AMD Phenom II X6 1090T processor.
I was able to reach just shy of 4.2GHz by lowering the HT multiplier again and increasing the CPU Voltage to +0.150V. It was benchmark stable, but only on lightly threaded applications. Keep in mind that this was done with air cooling, so as you can see even six-core processors are going to be fun overclocking parts. This is nearly a 1GHz overclock and is a success if you ask me!