Single speed #7s or #8s should do just fine if your leads are fair; if they aren't, bigger winches won't make life much better, as chafe & hardware strain will still be there. For even quite large boats, many sailors use #16s on the coachroof. One key is swing room, tho: 8" vs. 10" handle. If there's only room to turn an 8" handle, you may want a larger or geared (2 speed) winch.
We're moving the Enkes #20s (2 speed) from their place on the coamings, aft, up to the coachroof. They are undersized for sheet or afterguy work w/ a 750sqft spinnaker, or for kedging or use w/ drogues. The current Lewmar 40 primaries will move back there. The #20s are oversized for the coachroof, but we have them, and the 2 speeds and gear ratios will be nice with an 8" handle. One other thought is drum height: your lines should lead up onto the winch drum at 12 degrees or so. Small winches have short bases & may need to sit on risers to obtain that angle.