If you're going to put stats in str/dex past minimum requirements, don't do anything other than +15. A +15 weapon with 40 in its main scaling stats will always do more damage than its lightning equivalent.
I don't think bows get the two-handed strength bonus in this game like they did in demon's souls, so if you want to do the most damage it might be better to have a 40/40 Q build.
The dragonslayer greatbow is mostly used for trolling. It's entirely too slow for use in pvp, unless you're some kind of archery god.
The hawk's ring is only useful for extreme long-range sniping. If you're within lock-on range of your opponent, it's not doing you any good.
One other thing... actually landing headshots with a bow is damn near impossible, and they don't do much more damage as it is. I'm not sure if the hornet's ring increases headshot damage, but I don't think it does.
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edit: Shields specific to an archery build? I don't think there are any. Just use a shield you like. Same for weapons. I would use a spear or dagger just to keep with the theme, but that's probably not the best choice.