I decided to change my strategy for texturing the church. Instead of using one or two large image textures, I broke the model up into different materials. I am using procedural textures for the base materials and will use image textures for adding detail, dirt etc.
I also made more tests with Luxworks, Yafaray and Blender Internal. I think that Yafaray still looks the best despite the deficiencies.
Here is a sample: