For Ramsey Rev. D you simply change the Ramsey speed jumper J851. This does exactly the same as the skip mode. 
Interesting point. That actually controls the DRAM refresh timing, so moving J851 in that way will change refresh time from 9.5µSec to 6.1µSec. Though there are still 5 clock cycles per memory access, and of course the clock speed remains the same.
Would be good to see the benchmark result of J851 in either position to see the effect.