Re descending,

Deeper section rims will tend to be affected more by cross winds, as valygrl points out.

The thicker spokes of the R SYS catch a bit more wind than thinner spokes, but I don't notice much difference.

It may be more about technique than the wheels- gripping the bars tightly, and fighting against being moved some by the wind both end up making you feel, and in fact be, less stable. As a lighter rider, you're going to get blown around- try concentrating your weight on the outside pedal in the down position, to keep the COG low, and a light grip on the bars.

You might also try lower air pressure. Over inflated = more bouncing around, & less grip. If I weighed 125, I'd probably be running 75/80, or 80/85.