Quick rule of thumb for max SPL....
With two 88dB efficient speakers placed away from the walls and 8 feet from the listener, driven by 400Wpc (peak), you get 109.3dB SPL max.
If you double the power, you gain 3dB SPL. You lose 3dB with half the power.
If your speakers aren’t 88dB, just add or subtract the difference, so 90dB speakers will get you 2dB more, or 111.3dB SPL.