The way I've had cas vs speed explained to me is like this
ddr2 800 cas 4 = ddr3 1600 cas 8
so just check the ratios cas to speed
something like 8/1600 = x/2200 so x(or cas) = 11
for the 1600 ram cas 9 is already slower then standard.
cas 8 ddr3 1600 = cas 11 ddr3 2200
the cas 10 ddr 3 2200 is the fastest overall...assuming its stable.
Hope that was not super confusing, and please correct me if i'm wrong folks I know other factors apply in selecting ram but this is the general rule I’ve used.