have 2 Asrock boards, the original dual/Vsta and the 4core/Vsta. You will be able to effect a mild overclock but nothing very astounding. Your e6300 is going to be a limiting factor with it's multiplier being only 7. I have the same ram as you OP. You dont mention your gfx card so I'll tell you about both agp and pci-e. These are my settings.
I'm using the stock hsf and 8hrs orthos blend on the hottest day of the year never over 60c
On the cpu bios page
cpu pci-e = async
cpu freq = mine is 8hrs orthos stable @ 294, start a little lower (ie 285) and up it if you find it's stable
pci-e freq = if your card is pci-e dont go higher than 109mhz esp if you've sata h/d's as you can get data loss (sata uses the pci-e bus)
If you have agp gfx then 117mhz was recommended to me and worked well but that was with ide h/d's, same advice about data loss if you've sata drives.
pci = 33.3
spread spectrum = auto
boot faliure = enabled
my multiplier is 9 (e6600) OP's will be 7 (e6300)
max cpuid = disabled
intel virt = enabled
cpu thermal = enabled
non execute = disabled
speedstep = auto
on the chipset page
dram freq = auto
flexibility = disabled
everything else = auto except command rate which is currently 2T (not tried 1T yet)
dram voltage = low (which is 1.8 volts, the voltage of your kingston ddr2 pc667 ram)
Google for a prog called hwinfo32 which reports the correct mem and voltage settings on this board, it's shareware but works without limitations after you click through the nag screen. My report shows that my cpu is at 2646.7mhz and memory is at 294.1 and 4-4-4-12 timings.
Check stability with a prog called orthos by Johnny Lee (it's prime 95 for 2 cores)
Run orthos for about 10mins at a time whilst upping the fbs a few mhz in the bios each time until you start to get errors, then back off to your previous stable fsb and see how long it goes without error. If you can get to 8hrs then your set to go.
I found that agp gfx and ddr1 ram allowed me to run stable at 300mhz but after upgrading to pci-e and ddr2 I've had to lower my fsb to 294.
Assuming you can get to 290fsb then your e6300 will be at 2030mhz, your limiting factor being the 7x multi of the chips 266bus.
The e4400 would be the best clocker for money on this board with it's 200mhz fbb and 10x multi. At 290mhz that would be at 2.9ghz.