I agree I have several perfect pokemon that unfortunately came out with a crappy move-set so just keep plugging away and evolving 95%+ because the difference between 95 and 100 is minimal as long as the move-set is strong.
Yeah it's actually less than 2% from 100 to 91.11
My current Gyarados are all level 32.
2367 CP - 100 IV
2356 CP - 97.78 IV
2345 CP - 95.56 IV
2334 CP - 93.33 IV
2323 CP - 91.11 IV
Basically a 1.86% drop in CP from 100 to 91.11 IV.