Overclocking is all about experimentation and some risk to your hardware is involved.
Do you mean you are unable to set higher than 210 in your BIOS or that is the highest you have successfully run your system at without crashing?
It's true that your motherboard is probably capable of running much higher than that but maybe your CPU or your RAM isn't. Tweaking voltages, memory timings, and lowering the CPU multiplier may help but ultimately you are going to be limited by the quality of your RAM and it's capabilities will vary from brand to brand and stick to stick.
Two identical setups out of the box are always guaranteed by the manufacturer to run at design speeds but the maximum speeds each component will actually endure is always going to be unique.