A standard motor there is little point going past 5,500 rpm
A worked motor, carby, cam and balanced 6,500 to 7,000 rpm
A well built motor can rev to +8,000 rpm but that's gonna need a big cam, valve springs and correct valve timing and trick ignition timing.....an then see how long it lasts
On another point older When engines wear in the bore, they leave a ridge around the top of the cylinder and the bore gets worn unevenly from friction on the up and downs stroke. - a new younger owner will rev the ringer out of their new ride... At high rpm and heat the pistons and conrods can stretch slightly allowing the upper ring to contact the old ridge resulting in compression ring damage or failure
The sames goes for the enlarged bore, the rings expand and contract and over time this can result in ring failure or excessive oil use....
_________________  
|