edward was trying to do 3:4 BE to AC, i'd say he is trying to get a good deal, but strap was doing 1:1 in his res exchange.
The fact is that AC are overall more useful, so you I imagine the best deal you would get would be from Edward, 1:1.5.
As far as PS strap was doing 2:1 ps to AC, and I think that is probably the best you will get there as well. Maybe someone will do 1.5:1, but it's a toss up.