I used to sit next to a guy who previously professionally wrote compilers for both DEC Alpha and Itanium (http://robert.muth.org/ http://robert.muth.org/), who

I used to sit next to a guy who previously professionally wrote compilers for both DEC Alpha and Itanium (http://robert.muth.org/ http://robert.muth.org/), who mentioned that programs often ran faster on Alpha (which only supported 64-bit addressing) when modified to use 32-bit array indexes instead of pointers, due to reduced memory bandwidth/cache usage. Of course, one had to first determine if one needs to use any arrays larger than 2^32 elements.