sorry for late answer, not received your message.
I can't test igpu configuration anymore because with latest kernels (3.12
and 3.13) after switching to --px-igpu xorg does not start at all
latest messages from xorg.log are
[ 638.585] (II) LoadModule: "fglrx"
[ 638.585] (WW) Warning, couldn't open module fglrx
[ 638.585] (II) UnloadModule: "fglrx"
[ 638.585] (II) Unloading fglrx
[ 638.585] (EE) Failed to load module "fglrx" (module does not exist, 0)
[ 638.585] (EE) No drivers available.
[ 638.585] (EE)
Fatal server error:
[ 638.586] (EE) no screens found(EE)
[ 638.587] (EE)
Please consult the The X.Org Foundation support
at http://wiki.x.org
for help.
[ 638.590] (EE) Please also check the log file at "/var/log/Xorg.0.log"
for additional information.
[ 638.591] (EE)
