I think you can intercool it no matter how much boost you're running. But if you do intercool it you can run more boost then 8.5psi and your engine will be safe..Thats why people usually get intercoolers, (usually front mount intercooler's for cars, not sure on the X) so they can run more psi and keep the engine cool and safe. Like 18psi on properly tuned up imports. Of course at that much boost alot of the engine internals would be replaced by more durable components then stock, and then of course big brake kits, and suspension kits to adequately handle the added power.