power up which raikou?

if you plan to max it 15/10/15 for the last breakpoint against vape. if you don't plan on maxing it the 13/15/15

Do the 96IV...I myself powered a 12/15/15 Zapdos lol

The reasoning is usually: If you can hit the final breakpoint for Vaporeon/Suicune, you are good enough to take it down with ease anyway, there's no point to fuss about this unless you want to smash a record time for soloing vaporeon or something.

Group size and composition is a larger factor if you can gain the damage bonus or not (case in point, I regularly get +3 on suicune using only dragonites, in a small group), rather than hitting the final breakpoint for thundershock.

96% IV for me. Hell no that 2 IV difference is gonna matter for extra balls or success/fail in a raid.

I would go with 96%

89% definitely. I'm very OCD about attack IVs.

Both, but the 96iv if you only want to power up one.

Transfer both and wait for a 100%