Can there be such a problem or not? I know too small or not efficient enough is bad, but is there anything such as having an IC that's TOO big for your system? I imagine you would have some lag and it would take the turbo a little longer to spool if the IC wasnt the right size for everything.

 

Too small = boost drop. Too big = excess lag.

 

That's the short answer. The long answer is an improperly sized intercooler can cause all sorts of issues. It can cause your turbo to overrun just trying to meet its target boost pressure which can cause it to grenade. Another side effect is potentially blocking the engine radiator from getting the air it needs and causing your engine to overheat.