Starting with LAMMPS, there isn't too much to see out of the GCC 4.8 upgrade. However, when going from LLVM/Clang 3.2 to LLVM/Clang 3.3 SVN the boost is very noticeable. LLVM/Clang 3.2 was running about the same speed as GCC 4.7/4.8 but now with the latest development code for the Clang compiler it's significantly faster than the rest.
LLVM/Clang remains ever so slightly slower than GCC with MAFFT.
GCC also ate the cake when it came to the BLAKE2 cryptography benchmark.
The Botan results are mixed but overall LLVM/Clang 3.3 is doing very nicely compared to its predecessor.
In some cases, the LLVM/Clang 3.3 performance when using the same compiler flags as the other compilers is astonishing.