I have found Fedco trees to be a great place to get zone 4 and lower fruit trees. They have a number of peaches that are rated as Zone 4 and some warm pockets of zone 3. Reliance is one of these. On their website it says that peaches are self fertile, however you will notice an increase in setting of peaches with a secondary source of pollen, But it is not necessary.
As to my own encounter with reliance peaches, I planted mine last year. I have had almost no winter kill on the tips. It is also setting a huge amount of blooms. Coming from fedco the tree seems primed to realize the many fake springs that we encounter here on the high desert and hesitates to bloom until the spring is actually warming up. We had a pretty cold winter here, down to -20 with wind. I do not have any windbreaks. You can grow all fruit trees as a step over espalier. Which could be set at the height of the average snow bank. It also might help with windburn and extended winter problems such as sun scald. However some people have said it is more difficult to manage vermin like mice and rats. I have found growing fruit next to your house or other outbuilding increases their ability to overwinter in difficult cold areas. I really like writers who have to deal with variabilities in weather with fruit like Lee Reich and Michael Phillips, and for veggies Elliot Coleman and Nikki Jabbour.
I hope I answered some of your questions.
cheers,
Candice
