Well first, I wonder if there is a "right" answer to this question because "optimal strategy" would essentially be relative to each player's idea of what is and is not a good deal. Theoretically, any amount is good for B. For assuming he had nothing to begin with it's all positive expected value. "A" on the other hand is competing against other "A"'s so any loss to him may cost him the whole competition. If I were "A" I would push for a 80/20 split each time, hoping for a 75/25 negotiation and banking that no one else is keeping 75% over the long run. However, if I were "B" I would realize this and go for more by threatening to reject offers. "B" would have to reject about 25% of the offers to get a 60/40 split about 20% of the time. The math is loose but the idea seems solid to me.