I use warm water only because I want to maximize the shrinkage before hand. My washer automatically rinses in cold. Have you ever bought a pair of flannel pajamas that fit great at first, but noticed with repeated washing and drying, they shrink? I have, so thats why I use warm and dry in the dryer. I don't mind a little shrinkage in the finished quilt since I like an aged look, but a lot of shrinkage just distorts the patchwork. I know of some people who recommend several washings. I let the quality of the fabric and the results of the first wash determine if additional washing is needed (think quilt shop quality vs lesser quality) and I measure after the first washing to kind of guage the percentage of shrinkage. I also buy additional yardage to allow for shrinkage.
I hope this helps. I may be wrong, but I don't know of any standard guildlines about the amount of shrinkage to expect. Maybe quilt shops or manufacturers know that info.
Helen