I'll elaborate on this when I get back to work, probably next week, but in the meantime here's a few things you can try if you are having performance issues.
Both high-quality shadows and dynamic reflections can be heavy hitters, and while I recommend having both on, these can be tweaked to see if it makes a difference. Personally, I prefer high shadow settings, (with almost everything casting/receiving shadows) but this does slow it down a bit.
Dynamic reflections are use at NZCH, but I like low to mid settings rather than all the way up. This helps the appearance in some cases, as well as the performance.
On lower-end systems, you can set the scenery complexity to normal, and this will thin out the vehicles and clutter.
With the nearby city, with almost 140,000 autogen buildings and an estimated half a million trees, this can also tax some system, so try lower settings for both building and vegetation autogen.