basically if you take a (2) 10"'s and (1) 13" and give them any X amount of power.. the 13 will allways be louder than the 10's with that same x amount of power... (not concerning enclosures so we will say free air)
lets plug in some easy numbers starting with maximum potential(thermal rateing)...
@ max power: 2 10's using 800
@ half power: 2 10's using 400
@ 1/4 power: 2 10's using 200
Since you said X, and I know my math is a little rusty, but generally when X is used as a variable, it's the same in the entire equation, so uhhh if X=500 then 2x=1000, and since we're talking about 1 driver compared to 2, the 2x would be the 10s.
You're also assuming that the 13" driver will be more efficient, even with what you listed up there, you don't know anything for certain so you can't say x will be louder than y, because you just don't know.