what would my most economical choice be for nice size slices (family size)?
Define family size--like double or triple a wedding size?
I'm not sure-I would guess maybe double. The client wants "nice sizes to feed her family".
Oh that's a way different answer.
I sell a traditional wedding serving, 1x2x4. If she wants to serve a larger piece she orders more servings. So then she makes that determination of twice as big or three times as big and I charge her for every serving, ie double or triple.
So if it's 30 wedding servings a 10" is generous, a 13" is double, a 15" would be triple.