I haven't had a problem with overheating since I replaced the radiator and reduced the fluid level in the overflow bottle. But I live in Phoenix, AZ where a radiator can boil just by parking the car out in the sun during the summer.
But the car runs fine during the summer and isn't any more sluggish than can be expected from that powerhouse Olds 403 they saddled it with at the factory. But that's a temporary problem with a solution in the works.....