Hi Ray,
Just had a quick fly around LEBB but I'm afraid I don't see the dramatic change you are seeing when using dynamic lighting.
Frame rates are 20 to 30 - seem a bit lower when using DL but nothing dramatic.
GPU usage is around 50 to 60% with little apparent change when using DL. I am, however, running at a much lower resolution - 1920 x 1080 - on a much smaller monitor so maybe that could be part of the reason for the difference in what we are seeing.
Sorry I can't be of more help,
All the best,
John