I had similar issues and replaced my radiator rather than trying to flush it. Now my temperatures, rather than being 115C-120C, are around 85C-90C at freeway speeds with A/C on, ambient 95F.
You're running a little bit hot at 100-110C but it could be worse. Flush your radiator (disconnect rad, remove from car, pour in CLR, leave overnight, flush well), change your thermostat, change your coolant and you'll probably see a big difference. After consulting around many places, an "out of car" radiator acid flush (with CLR or HCl or Citric or whatever) is preferable to doing one in-car where the chemical can eat through seals and gaskets and so forth.
Congrats on having a working A/C in your car btw, apparently thats a rarity
