I've just basted a top in the warm and natural - first time I've used it as previously I used Hobbs 80/20. I must say it's beautifully soft and feels more stable than the Hobbs. I agree with the above - 4" no probs!
To add to Ninnie's comment re width, you can join batting together using a wideish zig zag on your sewing machine. If you make sure the edges butt up completely flat - no overlap and use 100 percent cotton thread, you can't tell when it's inside the quilt.
K x