optimization flags for simulation software

[yuvalif]

I have a C++ program that does an economic simulation. The program
have one function with many nested loops (3-5 levels of nesting), each
run in order of 10-1000 times. All loop limits are constants.
Inside the loops, simple calculations are done (exp is the heaviest),
and some global matrices are accessed (both for reading and writing).
The global matrices are very large ~10M.

I'm using floats for most of my computations. Accuracy is not very
important, and speed is the most
important, because I need to later find a minimum for that function.

currently I'm using the following compilation line:

g++ -Wall -fmove-all-movables -fmerge-all-constants -funroll-loops -O3
-o min_estimation min_estimation.cpp -lgsl

with the following g++:

gcc version 3.4.6 20060404 (Red Hat 3.4.6-10)

Do you have any suggestion for other compilation flags?
Would I benefit from upgrading to newer compiler version?

---------------------------
Yuval