Are you sure it's a real skeleton? There is an odd-generation bolt that was basically an old-stock Equalizer Pro but with window milling in the middle and a second tail o-ring added, and it weighs closer to 19.5g rather than the 11.5g of the true Skeleton bolt. The best way to tell them apart is to count the windows.
Granted, I did my testing on an Ion not an Enmey, but I found that the Skeleton was slightly more efficient than the L6, but that both were miles ahead of any bolt with a tail. I opted to install L7s on all of my markers because they were the 2nd best overall and I could afford that many Orange bolts (or find them for that matter).