> as gcc has matured, have the advances been x86 specific or are they also seen
> on other architectures?

You can read up on the changes between version 4.4.5 as available for MorphOS and the most recent version:

http://gcc.gnu.org/gcc-4.5/changes.html
http://gcc.gnu.org/gcc-4.6/changes.html
http://gcc.gnu.org/gcc-4.7/changes.html
http://gcc.gnu.org/gcc-4.8/changes.html
http://gcc.gnu.org/gcc-4.9/changes.html
http://gcc.gnu.org/gcc-5/changes.html

There, the changes are classified into language-specific, ISA-specific and OS-specific ones.