If you do go with peach extract, DO NOT use any of the "brewing" extracts. They are almost universally craptastic.
Go grab a quality extract at your local wholefoods/organic store instead. They are about the same price as "brewing" extracts, and much much higher quality. I've never used peach myself, but have used vanilla and black currant extracts that came out very authentic compared to the artificial tasting brewer's extracts I used before I knew better