Celestion data sheets show the Blue and Gold as 100db speakers, the G12H30 both Anniversary and Heritage as 100db speakers, but the G12M25 as a 98db speaker. Where we say "efficiency" they say "sensitivity", same as Eminence. The Eminence Red Fang is rated at 102.5db, but I have run a Gold and a Red Fang in the same 2x12 open back cab and switched back and forth with a footswitch, and can't hear a volume difference. I have also footswitched between Gold and H30, as well as Blue and H30, and felt that the Blue was louder than the Gold, which was louder than the H30, even though Celestion specs them all the same. Funny that the Red Fang does not sound louder, FWIW and damn my hearing... Part of the volume feel probably relates to the treble intensity, with the Blue being super bright, the Gold a little less so and the H30 (Anniversary 55hz) the least bright of the three but still very bright. The H30 55hz also has more bass than either alnico but less overall volume feel to my ear. I have compared the G12M20 to these above, but no longer have a G12M25 to compare. My guess is that the "2db" difference would be a lot more obvious from a Blue to a G12M25 than the small 2db spec suggests.