It's such a crapshoot to evolve. I know what you are thinking, you see the low'ish IV and are debating whether to power them up. So, like anything, it is dependent on what you need. If you need an immediate attacker, I would power up that DT/O despite it's IV. If you don't need an attacker immediately, and want a Defender, I would either evolve the 84% one that you have already that is at level 20 or wait for a higher IV dratini. Regardless of moveset, that one should get you respectable CP when powered up to place in gyms.
I had to 200+ candies, and just evolved a low level 95% one and got SW/Hur. Definitely disappointing. I am waiting to evolve another one with good IV b/c I really want DT/O.
