very nice to read all the discussions here.
of course with the current model ie 5D3 etc ISO >5000 can be really clean.
In terms of Tips for boring event, here i go,
1. Someone mentioned "tight" -> use longer focal length and move yourself (hopefully) to get some nice Background.
2. get some details rather than overall.
for Dark churches,
0. take RAW (I assume everyone (almost) takes in RAW)
1. Rule one for me, Prevent slow shutter speed (1/30 min -> depend on FL too). 200mm -> 1/60 min
2. If your cam body does not have a clean high ISO, I will go to the max (clean -> subjective) ISO then lower EV to -2/3. **This -EV here is to help increase the min shutter speed since I cant increase ISO. If you really cant maintain the min SS, "F it" and increase your ISO! Rather take sharp pic with noise than clean yet blurry pic.
3. Flash or no flash... of course if u can, then use it. Even if I dont fire flash, I ETTL it. (I am yet to experience churches that forbides flash but I have never fire flash in churches. I want to be as slient as possible.
If the above dont work for you, its time to upgrade your camera body.
Hope that's helpful.