To hit that +4 dBu, you would need either sensitive mics or a very loud source or, most likely, a combination of the two. The mics people here typically use are in the 10 - 15 mV/Pa range; with those, it would take a really loud signal (~ 133 dBSPL) to overload the F3 mic input. Some mics, though, are more sensitive (such as my DPA 2006s at 40 mV/Pa) and it gets more plausible. Put those things on stage, near the snare or bass drum, and it could definitely overload.
I believe the F3 has P48 on the line input? If so, you could just use that and your chances of overloading the input are tiny.