Note that the boost is only as dramatic for programs that make very heavy use of pointers. For instance, the benchmark that gets a 32% boost [1] requires "about 100 or 190 MB" of memory on 32/64 bit, respectively. If we call the memory used for pointers A and the memory for other data B, then this means that

    A + B = 100
    2A + B = 190
    => A = 90, B = 10

So if 90% of your memory usage is pointers, this is great. But I don't think that this is a typical workload. Otherwise, the performance advantage is not as clear.

Wikipedia notes that "On average x32 is 5–8% faster on the SPEC CPU integer benchmarks compared to x86-64 but it can as likely be much slower. There is no speed advantage over x86-64 in the SPEC CPU floating point benchmarks."

Perhaps the reason that no tier-one Linux distro ships with x32 images is that the additional complexity of supporting an additional ABI is not seen to be worth the modest performance increases.

[1]: http://www.spec.org/cpu2000/CINT2000/181.mcf/docs/181.mcf.ht...