Im not too smart when it comes to OC... only got family desktop with e6300 to actually test on.. with that i just raised the FSB and went from 2.5 to 2.75 on stock cooling/voltages.
With the athlon, just pump up whatever it is... BCLK? 5% at a time, then run some cpu benchmarks to make sure its stable, and repeat, if unstable, put the voltage up by one option at a time, if still not stable put clockspeed back down. if stable, raise again by same ammount as original and repeat etc
Front Side Bus (FSB): This is where you will achieve higher CPU speeds, as FSBx CPU multiplier = CPU speed. The problem with this limitation, is that the FSB decides the speed of other parts of your motherboard. Memory speed is FSB x memory multiplier.NorthBridge (NB) frequency is FSB x NB Multi. Hyperlink Transport (HT) frequency is FSB x HT multi. The HT multiplier often has to be inferred. It is often rated at a speed, which is the multiplied value at FSB of 200. Therefore, 2000 HT is 10x multi, 1600 is 8x multi and so on.
If any of these values is too high/low, you will have issues in the form of crashing, freezing, or refusal to boot. Fiquire out how to reset your Bios. I have a gigabyte board with duo bios for backup, so I have never had to manually reset it, as it automatically does so when the computer refuses to post. Handy .
With my CPU and motheboard, default NB is at 10x, and the HT is at 2000(10x), so when OCing the CPU, I adjust those multipliers to try keep it as close to stock values as I can.
My memory is rated for 1066 (5.33x at stock) but since I increased the FSB, I had to drop it down to 4.00 to keep it within it's stable range.
You raise the FSB in increments, lower multipliers as needed, and increase CPU voltage as needed. If you leave CPU voltage on auto, the motherboard will usually feed it much more than needed, indusing extra heat and limiting your overclock. Manually adjusted voltages will usually stabilize your CPU at higher speeds without the heat that auto induces.
I can recommend a few settings to start with, but you need to understand what is going on in order to make it stable, as no two computers perform and react the same, some do well with no extra volts, some need a lot. Some memory overclocks well, some doesn't.
3.0 ghz would need an FSB of 231, NB of x8/x9, HT of x8/9, A step down from top memory multi (most likely unless really nice memory) and would probably run off stock or slightly above voltages. Maybe.
Gleaning some anecdotal observations, the athlonx4 chips can reach some good speeds easily, or they can be duds that refuse to co-operate with even very mild overclocks. It may have been the motherboards, as generally the athlons are paired with cheap units (as someone willing to shell for a good OC board will probably step up to a phenom BE) or it may be the variance in the chips. There is no real way to tell.
If you get a 620, you might very easily achieve a 3.0-3.2ghz overclock on very safe, low temp settings. You might also struggle to break 2.8ghz.
I don't like using Easy Tuned for overclocking. I've tried it when overclocking my X2 5000+ and didn't get nearly as far as I did with BIOS overclocking. Anyway, yeah just follow some overclocking guides.
I would sugest this for a stable set up of 3ghz and can might can get you to 3.25 if its able too.
Stock max voltage is 1.425 (make sure your MB is not trying to over volt it like my always does)
FSB: 250 (AMD FSB is just a number for reference)
NB multiplier:x8 250x8 = 2000 stock is stable
HT multiplier:x8 250x8 = 2000 I believe this is stock and stock is stable =)
Ram: lower 1 level (ie from 533 to 400 (with a 25% OC its brings it back up to 500) or from 400 to 333 (416 after OC)
CPU multiplier: This can be lowered from 13 but not raised above so...
This keeps most everything at stock, except the ram which is very close to stock and your CPU that you want to OC. Watch your temps and voltages. Check for stability and your good =)
I have a 630 at 3.25Ghz max temp is 52c (speced max is 72c, I wouldnt go about 60c) and at stock 1.43v max load voltage (my MB auto increases voltage as load increases.) I am sure I could get 3.375 or .5 but I want to keep the voltage stock for now. (not using stock HSF either)