http://en.wikipedia.org/wiki/Surplus_labour#Surplus_labour_a...
"Exploitation occurs when those appropriating surplus labour — whether in the form of surplus-value, surplus product or direct surplus labour — are different than those performing surplus labour..."
There is no universal definition exactly but they share certain elements. In particular exploitation is the result of a power inequality between the laborer and the exploiter.
The question is not simply about the split of profits between capital investors and laborers. (Since capital is the accumulation of surplus labor, it's already exploitative.) The original act of exploitation it's self occurs much earlier. When you do not receive renumeration equal in value to that of your surplus labor.
Putting real numbers to those values is hard and I don't really have a satisfying answer to give you. You might find Elinior Ostroms work interesting though. http://en.wikipedia.org/wiki/Elinor_Ostrom
Simply paying more isn't the same as not being exploitative, even if it does make you feel better about yourself. I suppose it might make sense to consider the wider picture too, like how much of that increased income is produced by more fully exploiting other laborers.