As I said in step 3, you don't need to test the configuration via SaX2. 3D should be configured automatically. Unfortunately, SaX2 doesn't understand it any more for some reason. The way to check if you have 3D acceleration is not via SaX2, but by running

glxgears | grep direct

The output should be

Direct Rendering: Yes

Now, for the i810 driver which should be properly configured if you followed the steps above, you should have in your xorg.conf file the following in the section "Device" with the BoardName and BusID options different since you have the 855, not the 915 as I do

Section "Device"
BoardName "915 GM"
BusID "0:2:0"
Driver "i810"
Identifier "Device[0]"
Option "NoDDC"
Option "LinearAlloc" "65536"
VendorName "Intel"
EndSection

The option LinearAlloc specifies the memory used by the graphics card. In my case, I have set it to 64MB ( 64*1024 ).

To go back to the "intel" driver, just use SaX2 without any extra arguments. For the "intel" driver that ships with 10.3 I'm afraid I do not know how to manually allocate memory.