GCC 4.5.0 was running at about the same speed as GCC 4.4.0, which was slightly ahead of GCC 4.3.0 with the LAME MP3 encoding performance.
GCC 4.5 was slightly ahead of GCC 4.4 and 4.3 with the x264 H.264 video encoding performance.
With the CAMELLIA256-ECB cipher test in the Gcrypt library there was a dramatic speed-up between GCC 4.3 and 4.4. However, with the 4.5.0 release it appears that its performance has regressed ever so slightly, but still it is well ahead of where it ran with GCC 4.3.0.
There was not much change in performance with OpenSSL across the GCC 4.3/4.4/4.5 builds.