Your motherboard contains the SiS661FX chipset which means that at least you do have locked AGP/PCI ratios but you do not have Vcore/DDR/AGP voltage increase settings which will lower your ability to gain a maximal overclock. Also, if you flash to the newest BIOS you will lose your ability to play with your memory timings.
At this time only the motherboards that have the Intel chipsets give maximal overclocks with Nvidia being second and the Via/SIS/ATi being last.
It also lacks a CMOS jumper so if you have problems with the overclocking you will have to remove the power plug and remove the CMOS battery to clear the CMOS. At least the poles are there, just no jumper
My personal opinion is that for a value based motherboard you have allready made a decent (if stable) overclock. Should you wish to get the most overclock goodness on your next purchase you might wish to post here for some advice on motherboards.