Well im now questioning the performance compared to my old LA b2 250.1
The LA amp has 2 15amp fuses while the Pyramid has only 1 20amp fuse. So that means LA is putting out 420watts(30x14volts) and the Pyramid is putting out 280watts(20x14volts)
If you use P=IxV, your measurements would be correct, but lets get a bit more technical and (hopefully) more accurate...
If each is single channel...
Lightning Audio: 30x3=90 (times by 3 since the average music signal requires about 1/3rd of the average power in a test tone) then 90x13.8=1242 (I'm going to use 13.8 as alt voltage) then divide by two to account for amplifier inefficiency and it's 621watts
By the same method: Pyramid: 20x3=60 then 60x13.8=828 828/2=414watts
If you had more than one channel per amp, you would take the final value and just divide it by the amount of channels.
I haven't done this for a while so if anyone sees something, tell me. I think the thing I botched on is including the ohm impedence... Also, the fuses are only going to give a rough estimate of the exact power output anyway, so be aware that those values aren't exact.