90/110/80/100/80/95 (555 total) - Current stats
Speedwise, I'd love to say 112 to outspeed Thundurus, but we can't make it as fast as a fat kitten (Purugly), can we? It really doesn't gain any benefit from outspeeding 110s, as they are basically all resist both or are immune to 1 of his STABs or are useless in OU. What it really gets from that speed tier is outspeeding MGross and Gengar. Outspeeding 108s gets it over the four cavaliers, allowing it to beat non-scarf Keldeo variants. I'm going to go with 110 for now, as a flaming dog should be able to run as fast as a mouse, right? No? Whatever.
110 attack currently allows it to OHKO or 2HKO most top things that don't resist all of its attacks (Jolly LO set). Offensive Talons are an OHKO, Heatrans that don't invest in Defense are an OHKO, Clefable and Rotom-W are 2HKOes (usually). Skarmory is just under an OHKO, but Sturdy is a thing anyway. You can guess Scizor and Ferrothorn's fate (although the recoil and passive damage from killing a Ferro might KO Arcanine). Tank Garchomp is a problem, as is Landorus. But it's nothing I'd be too worried about. Plus, 120 didn't even make a huge difference in my calcs. I'll say Leave it at 110.
As far as defenses are concerned, I would move some of its split stats (especially Special) into HP. This means he can take more recoil damage before going splat. Without calcing anything, I'd say throw 15 SpDef (leaving him with 65) and 5 Def (75 left) into HP, conveniently leaving us with yet another 110. This emphasizes the glass canon archetype while not making it kill itself every 5 seconds.
Lastly, 555 is a great total, so everything we put into Speed is coming out of SpAtk.
Final Stats (subject to change after I do some calcs) - 110/110/75/85/65/110 (Total 555)
Again, these are glass canon stats. If we WANT defensive RK9, then go ahead and do whatever you want.