Have you made adjustments in the UI in regards, especially in these areas: Cloud Detail Cloud Draw Distance Cloud size Also as noted in numerous other posts Crepuscular rays are an expensive feature and to maintain constant frames you may want to turn them off... Additionally for more performance you can choose different texture sizes for the cirrus layers and overcast layers.... We included these variables and with a variety of hardware determined that you could attain better frames....... Additionally you need to take into account outside resources like custom scenery/aircraft and mesh all these factors have an impact on performance with or without SkyMAXX Pro....