the only difference between OBD I and OBD II is the amount and strictness of emissions controls.

OBD I is less likely to be upset by modifications, and you can reset the ECU and clear any codes yourself.

OBD II cars are easier to diagnose if there is a problem because all emissions components are so closely monitored. but, contrary to belief, you cannot erase a code from an OBD II car by disconnecting the battery. you may turn off the light, but the code is still stored in the computer and will come back the second it sees any "glitch" in operation.

but performance gains between the two are negligable.