I did a berries hefe last month and in 3 gal I added 2# strawberries, 1# raspberries and about 400ml of pure blueberry juice. It finished super dry and you can clearly taste the berries, not really subtle but really tasty. I also did a belgian dark strong and took 3 gal and added a 3# can of sweet cherries from noble grapes and yet on this one the cherry flavour is really subtle (still in secondary)
I guess it depend on the style of beer and the kind of fruits. my guess is a pound of apricot per gal would be perfect, the same ratio with raspberries might be not so subtle imo but personally I would still do the 1#/gal
