Personally I would not want insulated gear for backcountry / mountain riding. Being able to "layer" your clothing for high activity is key to staying comfortable and dry!! You also have the ability to adjust your layering to compensate for the changing weather conditions and your own body conditions as mentioned. The more layers (proper layers) also act as a sweat trap and can pull the sweat from your body and get it off your skin. This in turn keeps your body temp more regulated which obviously keeps you more comfortable.
It seems that most people that ride with insulated gear, do just that, insulated gear and don't layer enough. This can be okay as long as your body temperature doesn't fluctuate or change much.
Me personally, I would get too warm, which equals more sweat, which in turn is uncomfortable and leads to getting cold!!
I have buddies that run insulated gear and I also have insulated gear but this stuff is typically used for back home when the temps are down and so is the overall activity while riding. Trail riding, ditch blasting, then yes insulated or more layers. Keep in mind even with insulated gear, I would still run some kind of layers and most important....................NO COTTON!!