Sabertooth X79 and GSkills Ripjaw Z not clocking to 1866

I just set up a new system based on a Sabertooth X79 MB. I bought a 32GB kit (4x8) of GSkills Ripjaw Z, 1866MHz.
My bios sees the RAM, but with clocking set to Auto it only runs it at 1333MHz. When I set it to manual - 1866, the system becomes totally unstable (no video and machine continually rebooting itself). I cleared the CMOS (the little jumper) and then reset the RAM clocking to 1600MHz and the machine seems stable now (at least in the bios, i don't have an OS installed yet.
The ASUS guy tried to tell me that because my specific RAM kit isn't on the QVL, they can't guarantee it will run at the rated speed. But there are hardly any 32GB kits listed on the QVL!
Questions
1) should I be surprised that my RAM is not running at the speed it's rated for? Does this suggest something is defective?
2) would I be better to exchange this RAM for actual 1600GHz RAM, or is underclocking the 1866MHz RAM just as good? (keeping the faster RAM and underclocking it saves me a restocking fee).

 

solved

Someone from Tom's hardware answered my question. I had to activate XMP in my bios and then it was able to auto detect and load at the correct 1866 speed.
I can't believe I spent half hour on the phone with an ASUS tech and he never suggested this He basically said "sorry you'll just have run your RAM slower because that exact model is not on our QVL". Where do they find these guys??