Another vote for the M3. Despite the specs, I found the M3 to be a bit more efficient than even M60s -- when A/B-ing them I had to turn the volume down a bit for the M3s and up a bit for the M60s.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8