Resistance is less efficient the more it goes up.
1-50 reduces damage by 1% per point (50=50% reduction)
51-100 reduces damage by .5% per point (100= 75% reduction)
101-150 reduces damage by .25% per point (150=87% reduction)
151-200 reduces damage by .12% per point (200=96% reduction)
So around 250 you reduce by 100%. It is very difficult to become completely inmune to special damage.