my mantra: trust but verify
my other mantra: death by 1000 cuts
you have all the pieces, and this should provide adequate cooling. but maybe you've got a little off the ledger across the board: radiator is partially clogged internally or externally, t-stat wasn't working just right, pulley is just a bit off size wise, the thermostatic clutch isn't operating properly, you've got the timing off a little one way or the other so it's adding a little more heat at idle.
give each of those 5 degrees to play with, and you're +25 and into that 225~230 rather then 200~210
it has the capacity to cool, as evidenced that it runs cool on the highway. now to figure out why it doesn't work at low speed.
personally, i'd probably throw an electric fan at it before splashing the cash for a whole new radiator.