for /l %i in (1,1,1) do @start /b /affinity %i rscript 
-e"system.time(for(i in 1:1e4){fisher.test(matrix(c(200,300,400,500),nrow=2))})"

   user  system elapsed
  62.24    0.00   62.68

for /l %i in (1,1,2) do @start /b /affinity %i rscript 
-e"system.time(for(i in 1:1e4){fisher.test(matrix(c(200,300,400,500),nrow=2))})"

   user  system elapsed
  65.49    0.00   65.60
   user  system elapsed
  65.19    0.01   66.13

for /l %i in (1,1,3) do @start /b /affinity %i rscript 
-e"system.time(for(i in 1:1e4){fisher.test(matrix(c(200,300,400,500),nrow=2))})"

   user  system elapsed
  65.61    0.06   65.94
   user  system elapsed
  65.75    0.03   98.98
   user  system elapsed
  65.55    0.00   99.30

for /l %i in (1,1,4) do @start /b /affinity %i rscript 
-e"system.time(for(i in 1:1e4){fisher.test(matrix(c(200,300,400,500),nrow=2))})"

   user  system elapsed
  68.83    0.00   69.81
   user  system elapsed
  70.59    0.00   72.71
   user  system elapsed
  67.30    0.03  101.99
   user  system elapsed
  67.22    0.00  102.65