If the prop has too great of a load, what symptoms are expected?
Depends on which engine. Most 4-2 break engines will just lose performance before anything interesting happens to the engine itself. Piped engines, and modern ABC/AAC engines, most of them, particularly the big ones, almost can't be overloaded because they can swing massive props and the turn performance stops you from making them any bigger long before you get near the limits of the engine. I tried as much as a 14-6 on an ST46, that was clearly too much and I think I launched it at around 6800 rpm. But a 13-6 was not completely unreasonable.
Al Rabe told me he used as much as a 16-6 2-blade on his Jett 76 or 88, and I have no doubt that even the relatively wimpy RO-Jett 61 would have no problem with a 14-4 3-blade (and I have run a 13.5-4) if you set up for it. Of course, that kills the turn and provides no real advantage in propulsion, so I use a 12.5-3.75.
I have even seen people using am 11-4 3-blade on a *20FP*, and while it sounded like it was going to melt, it didn't, and pulled the airplane (a Flite Streak or something like it) marginally OK. That is rather beyond the pale, because we used the same prop on a piped 40VF! A APC 9-4 works a lot better!
Point being, the performance will go away somehow long before you cause any real engine problems.
Brett