the difference in performance from various compile options can be quite striking and are somewhat different for different programs.
the most important thing to optimize is the kernel (change the Makefile).
i suggest using
http://www.unix.com/source/unix_linux_bench.tar.gz
test with various comiler flags in the Makefile til you figure out what is best for your machine
what kind of CPU do you have -- perhaps we can offer suggestions
a word of caution -- lots of the information you will find in the Linux community online concerning compiler flags falls into the catagory of gcc mythology so test for yourself instead of believing others
another word of caution -- some compiler flags break certain applications either at runtime or break their build
it is very important NOT to try to optimize either gcc itself or glibc