Does it make a difference if my 4G iPod is on USB 2.0/Firewire or Mains Firewire when charging?

I usually put it on mains firewire charging, but does it really matter? (Undocked on computer).

Are the output volts/amps for USB 2.0 and firewire the same?

According to this site firewire it says firewire has 30V output

and according to here USB usb can power 500mA and if i remember correctly it has 5V output

i guess firewire would be faster and since the mains firewire charger is designed to simulate a firewire port the output and time taken should be similar.

just did a check the power adapter output is at 13V and 0.62A(620mA) so the mains would be faster than USB

Overall, your best charge will be obtained through the wall adapter. Charging from the computer was mainly provided to combat the power loss from the HD constantly spinning during music transfers.

If you must be connected to the computer the best choice would be Firewire.
The wall charger is good if you are only charging the iPod and not transferring data to it.