For what it's worth, I don't even bother investing in speed - I go for 252 HP 252 Atk 4 SpA. His bulk is more worth the investment to me since I play him expecting to take a hit and KO back instead of outspeeding and KOing (I wouldn't try to take on Landorus with mine though).
I would advise you to at least give it some speed. Most Gliscor usually invest in some speed and has the same base speed as Kyurem-B, I am sure you to OHKO it before it can use Toxic. Not that it could survive an Ice Beam or even switch in to Kyurem-B once its Special Attack moveset has been revealed.
My speed suggestion, not necessarily that I am a proponent of giving it more speed, is to give it some more utility against more offensive teams by outspeeding their key threats at the expense of its performance against stall teams. Kyurem-B simply is not as effective against faster paced offensive teams, since it usually would be outspeed, nor could it switch out often due it is nasty Stealth Rock weakness. Against more offensive teams, the best you can do is give it some speed so it does not become set-up bait once it is out, or use its natural bulk to sponge a neutral hit and KO back.
Still, it does have some merit to at least outspeed Mega Luc and Pinsir before mega evolution.
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interestingly, Life Orb Kyurem not only gives it more KOs against stall, but it is better against offensive teams, since it allows it to KO one of their Pokemon before it is taken down. Against offense teams Kyurem-B can at best hope to sacrifice itself while taking down just one of your opponent's Pokemon since it has fewer opportunities to set-up or use Leftovers recovery; Life Orb gives it enough power for KOs.
Perhaps against offensive teams, it can serve as an anti-lead, since it does beat Rotom-W, Lando-T, and Talonflame, if you are willing to sacrifice it. Sacrificing it to beat those Pokemon may be worth it, and at least you can disrupt their openings.