I am surprised by the problem that you have using the FA31mm and K-x. This is not normal IMHO.
I have shot several evenings in the local school hall. The lighting was poor and IMO poorer than in your church. (Rember it was evening time.) Using my K-7 and FA31mm (K-7 in hyper mode P), I got some excellent results of children dance photographs.
I use the following settings:
FA31mm in AF mode
K-7 dial mode in P (fully-automatic)
Auto ISO (with up to 1600)
For ISO from and above 800, noise removal with Noiseware.
After reviewing the shots, the shutter speed was typically 1/50 to 1/80 s and the shots look great.
In summary:
* you have a camera K-x with greater high ISO performances than my K-7. Do use this feature.
* try fully auto (dial mode P) incl. auto ISO
* the FA31mm is a great lens for this type of shots.
Hope that the comments will help.