I don't know the "transparance" speakers - but I can tell you a couple of things about "power handeling". First, 3 db of effeciency (1w/1meter) is roughly the same as doubling the power - so if they are less efficient than the jbl by even a db or two, you likely come out the same. Also, JBL rates conservatively.
second, you can put 10,000 watts into a toaster and it won't make any noise at all. its easy to build a speaker that will handle power, but hard to build one that turns it into noise.
Next, for an application like yours, your power amps should never clip. Its best to have power amps which are at least double the power handeling of the speaker. That will assure undistorted peaks, and save your drivers. Just don't run it too hard.
Next, on ohms, 4 ohms means the speaker will suck up twice as much power as 8 ohms. The amp will be delivering more power too. But don't be too quick to fall in love with chesaper watts.
Good power amps are key. They protect the speakers. If you plan on running both these subs off a single channel I'd suggest getting 8 ohm version. Even if your amp is rated to 2 ohms (the result of running parallel 4 ohm loads, you won't hear a huge difference, and you will stress the amp running it full out into its minimum rated load.
Basically, the best way to make more noise per watt is to use more speakers. trust me on this. Note most speakers will make the most of the noise they will ever make with ONE watt. note the difference between max spl and 1 watt/1 meter. Likely only 20 db or so.
If you plan on using "bridged" outputs, same advice. Bridging seems to give yu a lot more power, but the minimum impedance rating increases under bridging. If you bridge into parallel 4 ohm loads the amp will "see" 1 ohm, and unless its pretty special, it will thermal overload, or fry, or both. So, go with 8 and you have a lot more safe options. If you plan on dedicating a power amp to low end and running stereo, you can go with 4 and get more out of your amp, but most people don't run stereo subs.