Thanks for all your input.
LOL I wonder which lock in my guild equips
King's Defender! Envy him!!! I want it for fun too!
- I cannot afford to re-gem all at once. But definitely I'll re-gem some immediately (e.g. legs), and perhaps replace some epic gems with rare quality ones as interim solution.
- At the beginning of this post, my spell hit was at 211. Recently I downgrade from Gloves of Malefic and Anetheron's Noose to Enslaved Doomguard Soulgrips and Belt of Blasting, to sacrifice 1k hp+mana for more damage. After that, my spell hit becomes 230. After reading your suggestions, I may consider further reduce my spell hit to around 190-200, rather than cap at 202.

- I'll try to get Boots of Incantations. :D Thanks for tips!
- I usually equip Icon of Silver Crescent and Timbal's Focusing Crystal. I don't think I can afford the Darkmoon Card: Crusade.
The PVP trinket is only for Archimonde encounter 
- I'm going to stick to UA build, rather than go male/ruin, because my crit is pretty low. Besides, my guild's working on Vashj / Archimonde, dots are more useful in these encounters.
- About the spell rotation Siphon Life -> Immolate wasting 1.5 sec GCD. I deliberately do that, because I found my 3 dots (UA, Corr and Immolate) expire all at once with UA->Corr->Immolate->SL rotation. Switching the rotation and give me 1 second to refresh Immolate.
- I link my trinket with UA, so I should utilitize the trinket 100% with every spell rotation.
- Yesterday I tested at Dr. Boom with my spriest guildie and my dps is around 1150. My guildie found that there're 3 times in 5 mins I cannot keep all 4 dots (besides coe) up due to oom, and I have to LT/DP during T4 proc or trinket proc. That wastes the proc. How often do you LT/DP? Some suggest I should LT/DP twice whenever I'm around 5k mana. Some suggest I should always keep hp = mana.