When beginning with John The Ripper's MD5 test, the performance was not vastly different between GCC and LLVM compilers or between GCC 4.5.2 and GCC 4.6.0. On the Intel Core 2 Duo, AMD Fusion, and Intel Core i7 990X test systems, Clang and DragonEgg produced slightly faster binaries than GCC, but with the Core i3 2100 and Opteron 2384, GCC 4.5.2/4.6.0 was out slightly ahead.
With Blowfish on John The Ripper, across the five systems the compiler producing the fastest binaries was GCC 4.6. GCC 4.6 seems to provide faster performance here than the GCC 4.5.2 binaries on the five Intel / AMD systems. Using LLVM with Clang and DragonEgg for Blowfish is slightly slower than the tested GNU Compiler Collection releases.