First, you need to set the registry key to allow you to see Nero's realtime speed:
For Nero 6 follow these steps:
Start-> Run-> type Regedit
Go to "HKEY_CURRENT_USER\Software\ahead\Nero - Burning Rom\Recorder"
Go to Edit-> New -> DWORD Value
Rename "New Value #1" to "ShowSingleRecorderSpeed"
Click on it and select "Modify"
Now set the value 0 to 1
The next time you burn, you will see the speed at which you actually burn. It should go from 4 > 6 > 8 sequentially.
Second - you need to find out which media you are using and what speeds it will burn. Download DVD Identifier from here http://home.scarlet.be/~ping3828/dvd_identifier.zip
Put a blank DVD , run DVD Identifier and identify the manufacturer.
Third, DL NecDump from here http://freeweb.siol.net/tvajng/NecDump_1.0.rar
. Run the program, click Open and load the firmware file you flashed with. Click on Write Speeds and search for the disk make you have. It will tell you what speeds are supported for that particular media.