Go do some tests, see if you have a large consistency range of multistrike overcapping or how far it goes because in case of that, you would want to go Warsong. But if you are not near overcapping or if you only overcap doing a specific phase like burst phase, then Frostwolf would be better for you.
With tigger strike proc and trinket used i just hit 82% MS, never capping. With the 4p bonus, i am assuming that frostwolf must be better but in fact, as you said, i see as many warsong in top players. My head hurts ! But i guess the difference is negligible.
Also, i see a lot of stone of fire inc, is this a real damage bonus, or just needed for the survivability in mythic encounters ?
When I had scales and BHM I was over MS cap when everything proc'd with Tiger Strikes so I went with warsong. I just dropped normal Scales (I know sad right) for heroic DST last night so I may go back to MS on weapon after I sim it later.