Got my new SIGMA 100-300 EX APO IF F4.
A fantastic Lens, sharp wide open at F4. At F5 gets razorsharp. Highly recommended.
Mine is new, but not the DG version. Fast, precise focus, pure fun to work with.

My pictures of churches are all made with available light.
Some churches are rather dark, even on sunny days.
You often need a tripod, patience and time. High ISO doesn´t help.
You loose sharpness and depth in the colors.