I noticed with the older release of catalyst that my computer was slightly slower to start up when running on the integrated gpu.
With the last release (13.4), it seems to be worse: It takes 45 seconds more to start up when using the integrated gpu.
In /var/log/Xorg.0.conf, I have these lines that may help find the culprit:
|[||17.133] (II) fglrx(0): AMD Video BIOS revision 9 or later detected|
|[||17.133] (--) fglrx(0): Video RAM: 2097152 kByte, Type: DDR3|
|[||17.133] (II) fglrx(0): PCIE card detected|
|[||17.133] (--) fglrx(0): Using per-process page tables (PPPT) as GART.|
|[||17.134] (WW) fglrx(0): board is an unknown third party board, chipset is supported|
|[||17.134] Loading extension FGLRXEXTENSION|
|[||17.260] (II) fglrx(0): Turned off the discrete card|
|[||59.888] (==) Depth 24 pixmap format is 32 bpp|
Please fix it for the next release.
I have an intel hd4000 integrated gpu and an amd hd 7730m dedicated card.