From Primitive Performance, Dyalog ’13.

x←?1e6⍴1000

a. ¯1+{≢⍵}⌸(⍳1000),x     1.00
b. ¯1+{≢⍵}⌸(⍳1+⌈/x),x    1.62
      …

max=*x++; for(i=1;i<n;++i){if(max<*x)max=*x; ++x;}

SSE4 (Intel) or AltiVec (IBM), circa 2008