Mech have you seen these.
They are true RMS reading and the one meter measures Current and Voltage and can display either of these as well as power.They are only about $80 and made by a manufacturer thats been making reliable meters for decades.
viewtopic.php?f=60&t=6375#p108524 True RMS meters take thousands of samples per second and perform a mathmatic average to determine the true value.Wheras most simple meters simply rectify and filter to obtain the reading......they can be quite out and if you're multiplying two wrong readings , it can be very wrong .
BTW I was wondering how hard would it be to do a chart or graph like you did but display power verses Volts for each of the commonly available elements .
Say 1380W for the old still spirits
2000w for the T500
2200w for the game ones
2400 & 3600w for macs ones