diff -p -up boost_1_39_0/tools/build/v2/tools/gcc.jam.cxxflags~ boost_1_39_0/tools/build/v2/tools/gcc.jam
--- boost_1_39_0/tools/build/v2/tools/gcc.jam.cxxflags~	2009-01-14 15:31:12.000000000 +0100
+++ boost_1_39_0/tools/build/v2/tools/gcc.jam	2009-07-17 18:12:20.000000000 +0200
@@ -298,8 +298,9 @@ generators.override gcc.compile.c++.pch 
 toolset.flags gcc.compile PCH_FILE <pch>on : <pch-file> ;
 
 # Declare flags and action for compilation.
+local CXXFLAGS = [ os.environ BOOST_BUILD_PATH ] ;
 toolset.flags gcc.compile OPTIONS <optimization>off   : -O0 ;
-toolset.flags gcc.compile OPTIONS <optimization>speed : -O3 ;
+toolset.flags gcc.compile OPTIONS <optimization>speed : [ modules.peek : CXXFLAGS ] ;
 toolset.flags gcc.compile OPTIONS <optimization>space : -Os ;
 
 toolset.flags gcc.compile OPTIONS <inlining>off  : -fno-inline ;