Disappointing to hear about Freeze Shock, but I can live without it.When using Kyurem-B with maximum speed, 252 adamant Scizor will not OHKO you after SR, regardless of your nature.
That said, Kyurem-B appreciates the extra special bulk to tank most things rain teams throw at it so I personally would choose Hasty in your case.
Edit: I forgot to mention that, should you be able to keep of any kind of entry hazards off your field, the naive one actually survives one CB-Scizor Bullet Punch. I still would go with Hasty because Kyurem is just that good against rain mons and because I wouldn't want to compete against Scizor. That's just my opinion but now we know that a Hasty one has its perks.
Freeze Shock should be disregarded in OU as most battles are too long to restrict yourself to an one trick pony. Power Herb Freeze Shock is even inferior to something awkward like Gem boosted Fusion Bolt (do NOT try this) because Fusion Bold does not become dead weight after the first use.
I truly despise deciding between lowering Defense or Special Defense in general. I still feel uncertain about my Naughty Zekrom (not sure if I should've picked Lonely) but I was drawn to the fact that his Defense was higher and I didn't want to lower it, lol. Anyway, I actually have a MASSIVE amount of Pokemon lacking in Special Defense (tons of Naive) so I would lean towards Hasty, as you have been encouraging.
Kyurem-B attracts me because of his massive Attack stat, and I would love to focus on that. Adamant with 252 Atk would create a number that I would drool looking at, and using Scarf to mitigate Speed wouldn't bother me at all. At the same time, I enjoy Mixed attackers and wouldn't mind that at all as long as it focuses more on Attack than Special.Adamant is pretty decent since you can use the "ideal" ability for CB, and I guess Scarf set, as well as any physically based sets you would want to run in future. Careful is also a neat ability on Sub Hone Claws Kyurem, which is one of its better sets (imo Sub Hone Claws and Scarf are its best sets in OU) so I guess decide if you want to run a physically based Kyurem (pick Adamant) or specially based (you might want Hasty / Naive for that one), or a defensive one (Careful) and go from there.
Ginganinja, your thread was one that I was looking at recently. I naturally assumed that you posted the builds in order of your preference, so hearing that you preferred Sub Hone Claws and Scarf surprised me a little bit because they were later on in the list. It does push me a lot more towards Adamant, though.
Thanks a lot for your advice, guys. I am surprised and pleased at the great answers I've been getting, and any more advice is very welcome!