A DESCRIPTION OF THE REQUEST :
Linux supports since version 3.4 improved version of 32-bit ABI named X32
https://sites.google.com/site/x32abi/

JUSTIFICATION :
X32 has better average performance than 32-bit or 64-bit

results from some benchmarks:
181.mcf from SPEC CPU 2000 (memory bound):
Intel Core i7
~40% faster than x86-64.
~2% slower than ia32.

186.crafty from SPEC CPU 2000 (64bit integer):
Intel Core i7
~3% faster than x86-64.
~40% faster than ia32.