My initial impression of SMP4 is fairly positive--cloud rendering looks better than v3, frame rates seem to be no worse (or not much worse), along with a few other virtues. However, to my eye the precipitation does not appear very realistic. For one thing, it's hard to distinguish rain from snow because at least some raindrops seem to fall at an unrealistically slow rate, and (in my estimation) are unrealistically large (playing around with configuration options, per the manual, does not seem to have a significant effect). I've tested this under various weather conditions using www.badbadweather.com to find airports with moderate-to-severe thunderstorms, rain, snow, etc. Additionally, while on the ground I hear no sound effects for rain. I need to test more thoroughly, but my initial impression of the rain and snow effects are not too positive (just offering this as friendly feedback). On the snow side, I noticed immediately that my snow drift surface textures now move/change at hyper-speed with SMP4 installed; as though the wind is blowing at 200+ kts!
It would also be nice, perhaps in the future, to have the ability to adjust the rate of snow and rainfall (i.e., from light to heavy). Thanks.