Here are benchmarks of all major GNU Compiler Collection releases from GCC 4.2.4 through the latest GCC 4.8 development build. Benchmarking was of the seven GCC compiler releases from an Intel Core i7 "Clarksfield" system and an AMD Opteron "Shanghai" workstation.
GCC 4.2.4, GCC 4.3.6, GCC 4.4.7, GCC 4.5.4, GCC 4.6.3, GCC 4.7.1, and GCC 4.8 20120701 were benchmarked from the Intel and AMD x86 systems running Ubuntu 12.10 x86_64 development snapshot with the Linux 3.5 kernel. All GCC releases were built using the same compiler switches/flags. The Intel system had a Core i7 720QM processor while the AMD system was using an Opteron 2384 quad-core processor.
With this Linux compiler benchmarking being quite straightforward, let us get directly to the results. For those wondering how GCC compares to other Linux compilers, see my recent 11-way Intel Ivy Bridge compiler comparison. All benchmarking was handled by the Phoronix Test Suite.