Comparisons can be difficult because dates vary from year to year and between orchards.

Here's an orchard near Minneapolis (Zone 4) that publishes ripening dates for the around 75 varieties they have:

http://www.minnesotaharvest.ne...../dates.htm

And here's a chart maintained by a Wisconsin nursery that includes 124 varieties for Zone 4, 3, and 2, with information from a variety of locations:

http://www.edibleforestnursery.....AMESET.htm