the JBL would be fine. You are correct about the amount of power needed to reach peak output. Increasing the power will only cause them to reach full output at a lower system volume really.. which will only help if you want more bass in the music at lower levels.. this is mostly helpful if you want "feel it" bass at very low volumes. More power won't help in reaching a higher SPL much though, since at high volume you're going to be at full output from the subs anyway