Let me correct:
- 3.74 Mh/J is meaningless to us, because it is inflated by your inefficient baseline idle power of 150W (perhaps you have a high-power CPU, multiple hardware components not necessary for mining, or your PSU's efficiency sharply drops at low loads, or you are running a graphics-intensive Windows Aero desktop, etc)
- 2.62 Mh/J is meaningful.
I disagree for exactly the same reasons.
2.62 Mh/J is meaningless as it's not comparing like-for-like, you're adding in the unknown variable of the system, which will be vastly different (as you noted) system to system.
3.74 Mh/J is meaningful, as other people, who wish to compare their values, can use this number by factoring out their own baseline system power.