Go is not nearly as slow as you're making it seem to be, I dont know what the authors implementation was doing, but this code runs at a rate of 7GiB/s/core on my laptop

  func BenchmarkFindMax(b *testing.B) {
   ints := make([]int32, 13*1000*100)
   for i := 0; i < len(ints); i++ {
    ints[i] = rand.Int31()
   }

    for i := 0; i < b.N; i++ {
      max := int32(math.MinInt32)
      for _, x := range ints {
        if x > max {
          max = x
        }
      }
      dontOptimize = max
   }

   b.ReportMetric(float64(b.N*len(ints)*4/1000/1000/1000), 
  "GiB/s")
  }


  goos: darwin
  goarch: amd64
  BenchmarkFindMax-8  1530   678975 ns/op   7.00 GiB/s

EDIT: Actually my original code was reporting the metric wrong, it should have been:

b.ReportMetric(float64(b.N)float64(len(ints))4/1000/1000/1000, "GiB/s")

which leads to 9-10GiB/s on my laptop