I don't know how you managed to do it, but the performance in LOWW with the dynamic lighting option active and dynamic lighting active in P3D is AMAZING! I haven't tested much so far, but it looks good and performs excellently, both in an A2A aircraft and the MJC Dash8 Q400. I am running on an i7-2700K at 4.6GHz with hyperthreading enabled and and affinity mask of 245. My settings are by no means frugal and am using 8XMSAA instead of the more problematic SSAA (at least with respect to dynamic lighting).
You are doing something right that other developers seem not to be. Dynamic lighting can easily lose me 15-20 fps (I have nvidia inspector limiting me externally to 33.6fps). In LOWW, however, I cannot perceive the loss of even 1fps right now.
I hope this is not some anomalous, one-off situation and some other conditio is going to kill the perofrmance in-sim.

Cheers
Andrew