The interesting x264 H.264 video encoding benchmark at the version used could not build with GCC 4.6 or any of the LLVM solutions. Between GCC 4.2 and 4.5 there was no major change in performance with x264.
GraphicsMagick is another interesting test that uses OpenMP for its multi-threading work. GCC 4.4/4.5/4.6 were all much faster than earlier GCC releases and of LLVM-GCC / Clang. LLVM-GCC and Clang ran at around the same speeds as GCC 4.2.1/4.3.0 on the three test systems.
It is the same story with another GraphicsMagick operation.