HIGH MILEAGE CB500
Dshillz, Having put over 100,000 miles on a 97 RRV Fireblade a while back i would say the wear within the engine would be down to how it was ridden and service history. Chances are the engine would show no signs of smoking although it could still burn oil.
My concerns would be about the clutch basket. The fingers on the basket would be nibbled badly if not replaced.My Fireblade clutch pack was changed at 56,000miles and the basket was showing fair wear by then. Dipples on the plain clutch plate having been worn smooth would cause the gears to engage with a "smack" as these dipples help to slow the clutch down in the oil when changing gear.
First to second gear changes on any high mileage gearbox would show signs of wear on the engagement dogs. A good clutch basket and good clutch pack would help with gear changes but often get neglected.
Steering head bearings/ Wheel bearings/ Swinging Arm bearing and bushes take a battering on our crusty roads, so need to be checked carefully.
Front forks, Check for pitting and stone chips that could damage the fork seals and dust seals.
You must go through all the service history of any intended purchase and make sure all ive just mentioned has had attention at some point.
Also consider buying a lower mileage CB500 as there are plenty out there with only nominal miles.
Performance and fuel consumption: I would say the engine would still have a healthy sound to it when revved and depending on whether the bike is a carb model or fuel injection, would still return 45 mpg+.
Good luck with your decision.