Adam, I guess that you could use reflections for one or two planes, and enable the reflections in P3D options menu at same time. With aircrafts that not reflection enabled you should go for disable that option in P3D and everything goes fine. The update number 26 is out and seems to solve every problem that I noticed with 24 and 25! Thanks for the autor TS!!
I have an "old card": GTX 470 and my settings are 8xSQ and 2xSGSS. The image is amazing locked at 30fps I setup my clouds to 512x512 in my favorite weather program, above that it seems to start stutter a lot. AF to app controled and anisio at FSX marked on. Max pre-render frames to 1 because I have one graphic card. Bellow is a screen of my settings: