Few tips of mine for the lei shen 10m hc.
1 minute detterence is a must.
glyph of detterence is very useful if you are on platform that someone cannot solo soak but more or less it's not mandatory.
glyph of disengage - very useful especially with helm and p3.
As for the spec i have tried both and bm is definitelly ahead of sv (Even od ball of lightning because the live like 10s and dots dont even have time to fully roll on them) and you might time BW on them very well. They have like 50s timer or so, so its not that easy, but doable
Sv is only good for padding metters when someone messes up (usually on purpose) with the chains in p1/p2. But ele shamans are just better for this job
Fervor vs DB -> DB form me, there is only 1 time where actually DB is timed with tank moving boss with our tactics and i just dont like fervor with BM.
If you are playing right with your focus and will have around 80 before adds then you will be able to just MS,Barrage,CS,MS,KC,CS,MS with 100% Beast cleave uptime.
Barrage - GT -> it all depends of your raid composition, and how fast the adds dies, and dps needed on the boss. For me barrage was a minimal dps loss on single target, but on adds it just rocks. I have tested both, but barrage was definitelly better for my raid and my overall dps, with almost no loss on single target dps.
Intimidation is very useful on diffusion chains coz they hit hard as truck as someone mentioned, keeping them stuned and slowed is a good thing.