Detonation isn't caused by pressure, pressure is caused by detonation. And high octane fuel is actually harder to burn than lower octane... that way you can run more advanced timing and higher boost before the fuel pre-ignites (burns out of control at it's own will rather than when the spark is fired).
At our altitude a short ram is a pretty low risk. However, I can almost guarentee you're also not making any power out of it... just noise. In fact, until you're running more mods and engine management, all an intake does is make noise, risk lean AFRs, and cause the ECU to retard the timing.
Remember this as well, at something like 6000 rpm, the knock sensors turn off since they can't hear knock over the frequency of the motor itself, so you can run lean and *not* retard the timing. Ask me how I know...
