given memory that can both hit the same frequency the one with the lower cas should give more wiggle room to tune with.
that being said OP should really run some benchmarks to find out if a 25% decrease in fsb speed
is compensated with a 1/3 to 1/4 decrease in cas latency
I think stability will probably be one of the most important factors here, and whichever is the one that is most reliable should be chosen.
At the same CPU speed, the advantage of 2000 at pretty much any latency is going to go be 5% at best. However, if your OC requires that you go way past a 200 BClock, then get something faster than 1600 for sure so your memory is not the cap on your OC.