Bill tried to set you straight. In more layman's terms, about the only thing that is linear in the whole operation is the numbers 1 to 10 on the amp dial.
SPL is on a log scale to 'match' with voltage and make graphs possible to fit on paper. It also dovetails with how we hear changes in SPL.
If you know anything about power, it varies with the square of the voltage. Decidedly non linear!
While the heat remains under control you can get 3dB extra volume each time you double the power. A very non linear 1w 2w 4w 8w 16 32 64 128 256..... 512.. silence.
Rules of thumb might have changed a little in the modern high power woofer game but it used to be that around half the rated power through put was where they would start to get warm and go 'non linear' not that they were ever linear in the first place.
OP's 800w cabs will do very well with 480w each.