It really depends on the make of engine and especially how it was run and stored.

Some of the best engines (like OS) will fail early f not ran properly and stored properly. If an engine has always sat with unburned fuel in the crankcase and if it has sat for months or years between runs then the bearings will almost always fail early.
If they are tuned to run lean and at high rpm's then you can guarantee a failed connecting rod bearing and conrod breakage and/or early piston, ring, or liner wear is in the near future.