As long as the core voltage is not up around 1.600 V or so, you should be okay on a damage standpoint. On a stability standpoint, a wide voltage swing may cause issues. Sure, the computer might happily run at 2.8 GHz at 1.400 V, but what happens when the voltage drops to 1.260 V?
If you want to do your overclock properly, something I have never done, this is how you do it:
1) Reduce CPU multiplier to 5x, reduce HT Link to 2x, reduce RAM to 200:100
2) Increase the HTT by 5 MHz
3) Run Orthos 30 minutes
4) If it passes, go to step 2; if it fails go to step 5
5) Subtract 10 MHz from the HTT you just tried and write that number down as "Max HTT"
6) Return HTT to 200, increase memory to 200:200 (or in your case, 200:166)
7) Increase the HTT by 5 MHz
8) Run Orthos 30 minutes
9) If it passes, go to step 7; if it fails go to step 10
10) Subtract 10 MHz from the HTT you just tried and write it down as "Max RAM"*
11) Return the HTT to 200 and the RAM to 200:100, then set the CPU multiplier to its maximum (in your case, 10x)
12) Increase the HTT by 5 MHz
13) Run Orthos 30 minutes
14) If it passes, go to step 12; if it fails go to step 14
15) Subtract 10 MHz from the HTT you just tried, multiply it by the multiplier in step 11, and write it down as "Max CPU"
16) Return the HTT to 200 and the CPU multiplier to 5x, change the HT Link to 5x
17) Increase the HTT by 5 MHz
18) Run Orthos 30 minutes
19) If it passes, go to step 16; if it fails go to step 20
20) Subtract 10 MHz from the HTT you just tried, multiply it by 5, and write it down as "Max HyperTransport"
Now we know your maximum CPU speed, maximum RAM speed, and maximum HTT. There are a few programs available where you can input these three numbers and they will suggest the best course of action for you. You can also do this manually attempting to maximize the CPU speed and RAM speed knowing the limitations of your HTT. If you did the optional step, you may be inclined to try maximizing your HyperTransport (that is, preferentially keeping the CPU and/or RAM speed slower to ensure that HyperTransport is about 1000 MHz).
You will have links to said programs from someone else soon**. I always just played it by ear. Instead of worrying about the RAM speed, I worried about the RAM bandwidth. To test the RAM bandwidth, you will need a program like Everest Ultimate.
*Maximum RAM for those timings and voltage. Loosening timings tends to increase this value. Tightening timings tends to decrease this value. Increasing voltage tends to increase this value. Decreasing voltages tends to decrease this value. The effects are inelastically additive. A similar argument exists for CPU Voltage, which if your Via K8T is like mine was, is nonadjustable in your case.
**Gogar's A64 OC Optimizer for one