Um, yes it is an obstruction.
There are many possible restrictions to OCing and it just depends which one you hit first.
Memory and heat are probably the most common. Instability with expansion cards (AGP,PCI) are probably next.
The speed of the CPU doesn't matter. What is the original bus speed and what did you wish to OC to?
If you are only increasing a multiplyer then it will not affect the PCI/AGP bus'.
215 would probably mean 35.83 MHz for the PCI bus. That's not actually very far out of spec (7.5%), but you need to be careful with it nonetheless. The less devices on the PCI bus, the better.