I have two nearly identical pvp characters -- one EP and one DC.
The DC character wears Morag Tong + Hawkeye, all impen.
The EP wears Marksman + Hawkeye all divines (with Warrior Mundus)
In testing with a friend, I was seeing no difference at all in Snipe damage between the two. This shocked me as the second character with full divines AND two separate bow set bonuses should do noticeably more damage. Then it dawned on me: maybe the two bow damage bonuses don't stack?
So I changed the EP character to Morag Tong + Marksman (still all divines) and got about a 10% damage increase.
I was wondering why Alcast's bow gank build didn't recommend running both bow sets (he reco's using Morag Tong + one of the bow sets. I think I may have discovered why.