It is (supposedly) most likely at XXX, since the client will use old coins/transactions when sending 5 BTC from XXX to YYY.
Is this true? Do older coins get used first prior to newly deposited ones?
Why don't you go look in the source code and find out?
Edit: I don't mean to sound rude, I am trying to look at the source code myself now. Anybody know where this logic is held?