If you're upgrading your RAM for a gaming build, DDR3-1600 CAS9 (2x4GB) can be considered the sweet spot.
From the looks of the RAM that you've listed, I would avoid the single 8GB Vengeance RAM because I'm assuming your motherboard and system performance are better optimized with dual channel RAM setup of 2x4GB.
For the remaining two options, if you can get DDR3-2400 CAS11 performance at the same price as DDR3-1866 CAS9 then you're getting a steal of a deal. Frequency of the RAM plays more into performance than CAS timings.
I'll circle back around to my first statement and say that if you can save $15-$20 on slower RAM and put that savings towards a graphics card upgrade fund then all the better.