Difference between 1600, 1866, etc.

Solution
Yes, I've been building with primarily 1.65 high end DRAM for years now typically 1.6-1.65 (about 50 builds a year and all are purring sweetly), it won't hurt the CPU
For gaming, you will not likely notice a difference - a benchmark may show one speed as faster but who runs benchmarks all the time? Look for deals - get the one that is the best deal, or think looks better - it won't matter much.
-Bruce
 

Tradesman1

Legenda in Aeternum
Now your talking, big question with 2400 sticks is what CPU, need a strong CPU for it's MC (memory controller) for 2400 - What CPU, guessing Intel from the 1.65 comment - Intel recommends 1.5 for base level DRAM (i.e. 1600), however 1.6-1.65 is perfectly fine, INtel even certifies 1.6-1.65 DRAM for many of the 15 and 17 CPUs (primarily the k models)