If 1866 just costs a couple of dollars over 1600 there's no harm in getting it, but don't pay any real premium for it.
You might want to get a Cooler Master Hyper 212 Evo instead of the Hyper 212 Plus; the Evo is simply an updated version with better heat pipe layout and an improved fan (ostensibly).
Sadly tigerdirect.ca doesnt sell them. Is the Evo worth it though? I will be overclocking to 4Ghz, maybe 4.5.