ahh i thought that it was worded funny for port area. but yeah, i would say thats driver dependant. if you are saying SE 10s vs RL-p 15 i would say the RL-p
yes, as well as Bl, QTS, powerhandling and other factors, there's too many variables to make a blanket statement.
It is possible however to compare actual drivers and determine what would be louder when other variables are known (power, available enclosure space ect)
To an extent. Xmax is just another number in the equation that makes a woofer a woofer. You probably won't hear much between a 2-4 mm difference, but don't think a woofer with 10mm of one way throw is going to get just as loud as an equal woofer with 20mm.
Also it's box dependant. In my own experience, sealed boxes tend to work with the excursion of a woofer, while ported uses the cone area to it's advantage.
In this case, I think a lot is working in favor of the 15.