As Krilli said, the most loudness will be gained from more efficient speakers as decibels go exponential and power just linear....
And also as Krilli said all class T amps (and other amplifiers as well when the loss is accounted for due to their low efficiency) produce equal power at equal supply voltage. The only differences they have is some can handle higher supply voltage and can deliver more current which makes them more powerful. And some are bridge connected by default, some aren't and can still be bridged, which halves the amount of channels, but makes them roughly twice as powerful because they can output twice the supply voltage...
The best thing you can do, but very very hard to get is build up the amplifier with a symmetric isolated 12V to +/- 60Vdc converter. Common car amplifiers of higher quality have these. I have also started a thread about these before, but mind you these projects are not for beginners!!
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Pics can help a lot to diagnose something from any place on the globe...