Lucky you. I battled three yesterday, the first two ran away and then I caught the third one on the last ball. Ended up being only 11/15/14, but at least it already has Volt Switch and Wild Charge...
Well, to be fair, I had a perfect Thunderbirb ran away before, and only caught few Firebirb. My best catch there were only 43/45IV Freezerbirb and 42/45IV Lugia. This is indeed my best luck ever in GO, never any other time (I can only recall my best lucks were only an outstanding Larvitar at high level).
Well, I'd say -5IV is good enough to be kept and considered raising once beast migration happens again. After all Raikou is already better than any other electrics including Thunderbirb. We have a full month, but these beasts have
atrocious catch rate. To hit excellent curveballs with all balls is a must. I hope I can catch more since Raikou may be currently the best Electric non-cover Legendary across all generations, it seems (well, there's still insane-Atk Xurkitree
? but that's long and is pretty much glassier cannon than all-round Raikou).
Still, it'll eventually happen that one will catch very fantastic Raikou. Around 31 raids minimal is good, focusing on good attackers and throwing skills will very much help.
Now what I wonder is when Pokebank happens for GO (hopefully Masuda don't forget that). Suikun is useless here, but transferred to main games, a decent battler. Same with other legendaries (... well, at least the two NU birbs can be trade fodder....) and including those with subpar IV (viva Hyper Training).
Sorry, I kinda like using "birb".