3 cut up peaches in 5 gallons...you'll never notice it.
peach is a notoriously difficult flavor and aroma to extract...its just so delicate. every successful peach wine, beer or mead I've read about had two things in common: TONS of peaches, and they were hand picked, tree ripened peaches...not your typical grocery store variety. Farmers market, or personal orchard basically is the way to go.
and when I say 'tons' of peaches, I mean a minimum 3lbs of peaches per gallon of product....more for mead and wine.
all that info aside, normally you'd go through primary, then rack the beer to secondary, onto the fruit, give it a good couple weeks, then bottle, keg, or if its cloudy, do a short tertiary to help it clear.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10